Can't get up to 75 MPH!

Please help! My problems started 9 months ago when my family were on a canoe trip in Arkansas. My truck stuttered a couple of times on flat land but as soon as we started going up steep hills, the truck slowed way down. I pressed the pedal to the floor but nothing happened. I also can't reach 75 MPH. My truck accelerates good up to 60 mph until overdrive comes on. Then I have to press on the gas and that's when the passing gear kicks in. It's slow getting to 70 mph and then I press the pedal all the way to the floor and nothing happens. I replaced my o2 sensor and my air/fuel sensor, spark plug wires, plugs and fuel filter and cleaned my MAS air filter. I live in the Mississippi Delta and don't have any steep hills to go up to see if this all helped. I checked my c/c this morning after running it hard and it wasn't glowing. Can a bad ECU cause this?

 

how many miles? any CEL's?

it could be a clogged cat converter

 

Is it running rough? I know you just replaced you spark plugs but it almost seems like you arent firing on a cylinder or more than one.

 

157,000 miles, It threw a bad o2 sensor so I changed both. The truck seems to accelerate a lot better since I changed wires and plugs. Does the catalytic convertor glow when it is clogged?

 

it can but not always...usually they have restricted flow that can bog down the engine, did your code happen to be P0240 i think?

 

It was po420

 

will it rev up high when in park? if so, the convertor is okay. My truck did a similar thing (2003 v-6) and it was the mass air flow sensor (maf) the dealer would not warranty it under drive rain.

 

yeah i get numbers mixed up



id check your cat, especially if that code pops back up

P0420 Catalyst System Efficiency Below Threshold (Bank 1)

 

Just tried it. Truck revs up to 5000 rpm just fine. Is there any way to check the cat?

 

just get rid of the cat and you wont have to question it

 

If you get rid of the cats, will the sensors get mixed signals?

 

This happened on my mom's car once many years ago, it was the cat converter... Strangest thing ever, just clogged up and ran really rough... Replaced it and it was right as rain...

 

you can get a URD 02 simulator to fix that, are you in an emissions state/county?

 

Have you been using fuel injection additives in your gas tank? Some really tear up the converter unless it says on the label that it is SAFE for catalytic converters. This lady I knew messed up four of them because of this.

 

I'm not in an emissions state( all they inspect is the windshield, headlights brakes and turn signals and cost only $5.00). I added Amsoil fuel additive only once two weeks ago. I'll check into the URD o2 simulator.

 

The the tach go sky high but the speed isn't increasing? or the revs won't even increase?