High RPMs Driving On Freeway

Bought a 96 Tacoma 3.4 V6 MT 4x4 with 225k miles about 6 months ago. It's my first one and I really love the truck so far. It's basically stock beside 235 75 15 wheels and a camper shell I threw on. When I purchased the truck it came with basically all the maintenance records I could imagine it having since 96, I even have the original window sticker from the lot. I've kept up with regular maintenance thus far and have learned a ton reading through the forums here.

The truck seems to be running fine but I think my RPMs are a bit high on the freeway for the 3.91 gears that are in the truck. In 5th, at 65mph I'm running at about 2800 rpm and at 75 I'm at 3100 rpm. This seems higher compared to most trucks I've read about on here and what I've compared with the online calculators. Also, this thing is SLOW off the line, and takes some work to get going. Truck displays no lights and throws no codes.
Do y'all think the RPMS are too high and if so where should I start looking for a problem? Is it just the gears? I plan on re-gearing at some point so if it's just that I'll put off until I can take on that task. Thanks.

 

Sounds about right.

 

What’s your MPG.

 

Actually, not that bad, like 16-17mpg. I live in LA so lots of freeway and city miles. I'm going to buy an UltraGauge this week so I can know for sure.

 

With those small tires and a manual transmission, yeah those rpm’s sound about right. The 3.91 gears are why it feels slow off the line, these trucks just don’t have enough power to overcome the under-gearing. Extra weight from the camper isn’t helping either. It would feel a lot better and peppier off the line with 4.10 or 4.30 gears and 265/70 or 265/75 tires.

IIRC the carriers for 3.91 gears are different than for 4.10 and up, so if you go to regear be sure to check that or be prepared to buy new carriers (or better yet, lockers) to go with those new gears.

 

I suspect the tire size is contributing. Most v6 trucks I've seen came with 31's. That is about a 6% difference from what you have. That's about 200 RPMs at 75 MPH.

Also typically they came with 4.10 gears. Are you certain you have 3.91s?

 

I really appreciate the reply and all the information. I hadn't read that about the carriers being different so that's definitely something I'll have to look into. I've been playing around with the idea of a locker and I figured I'd have to re-gear sooner rather than later. It just seems so difficult for non TRD trucks.

 

Yeah it unfortunately has 3.91's in it (B06A) and it came stock with 225 75 15. I think it's kind of an odd ball. Maybe I just try 31's and see how it goes.

 

31’s would be a good first step and would reduce your highway rpm’s at the same given speed compared to the 235’s, however it will take even more time to get up to speed pushing bigger tires with the same smaller gears.

They did weird stuff in 95-97 especially, it doesn’t surprise me that your truck came with that strange setup. You could basically order a truck with any combination of features.

 

If you are going by what the door jam sticker says, not sure I'd trust that info for tire size. Mine says the same, 225/75r15, but from the factory is came with 265/70r16 and 4.10 gears (B03A).

 

Oh man, I was pretty confident but some crazy thing like that wouldn't surprise me. I'll jack it up later today and see what I can figure out. I read a thread last night that had good instructions.

 

Well I think thats what I'll do. The impatient drivers in LA can wait a little longer for me to get up to speed. I'll jack it up later tonight and confirm the gears but from what y'all are saying sounds like I just want to re-gear here soon

 

I’d go bigger tires before regearing. Regearing is probably going to cost you $2g’s

My 2.7L with 31’s and 4.30 gears is at 2,500rpm at 70, but I get 21mpg. (Lots of highway)

 

You might be able to find stock diffs from a 4.10 truck (easier to find) or a 4.30 (harder because less trucks came from the factory with these gears), which would be much simpler and cheaper, and would solve the issue of the carrier incompatibility from your 3.91 diffs.

 

The door tag says my axle ratios are 3.91. I have 31” tires and at 60 mph I’m doing about 2050 rpm. 70 mph is 2500 rpm and 85 mph about 3000 rpm.

 

Yeah there seems to be quite a few stock diffs on marketplace right now. I think looking for an axle with 4.10 or 4.30 gears and an e locker might be the move though. I know I'll want it eventually. I'm going to start with 31's for now and start planning on a re-gear. Thanks for all the help

 

I’m kinda confused, what are you trying to accomplish.

Taller tires will lower your highway RPM, but Lower Gears, numerically higher, will raise your highway RPM right back up.

And the V-6 pulls relatively well, unless you’re coming from something that has substantially more power.

 

Yep….31’s will make off the line worse but lower the highway rpm. Regearing will bring back the low end performance (which is already supposedly bad) but will also bring back the higher highway rpm and possible even higher than it is now depending on what ratio is chosen.

I wonder if there is a problem like partially clogged cat or something that’s making the acceleration so poor. The gearing as it sits currently sounds pretty good and if it’s a dog still, I certainly wouldn’t want to make it worse with 31’s, but then again it’ll be made better then with the future regear? Lol. Might be something more going on to look into.

 

I'm just trying to achieve some sort of balance. I'm going to add weight to the truck soon too and if I'm going to be terrible off the line with just 31s I figure more weight will just make it worse. So my thought process is get the 31s then re-gear before I add bumpers, skids, sliders, etc. I'm only in LA for another 4 months then moving to a place where I won't really have to do any freeway miles so I think going back to higher highway RPM is fine as long as it's not bad for the truck and it'll get me off the line around town a little better.
I like your idea about the partially clogged cat, I'll look into it. It was stolen at one point and replaced with an OE one if I remember correctly. I'll have to look at the maintenance records when I get back home but maybe there's something weird with that.

 

my 98 has the same gears. I run 265/75/16 so basically 32s. I have a 5 speed as well. I am at about 3000 rpm when going 75 or so but my speedometer at that speed is probably 5mph based on tires that are 3" bigger than the door sticker. Sounds normal to me.