motor/tranny vibration at 1500rpm?

So I'll try and describe this as best as I can. Hopefully someone might give me an idea of what it may be..
I have this slight vibration at about 1500rpm. It only seems noticeable starting at around 1300 up to 1600/1700 rpm maybe. And it only happens when accelerating. In idle it does nothing. Nice and smooth. This just started too. It is hard to explain but it mostly feels like a vibration kinda like a phone vibrates. Or how mud tires vibrate your truck at high speed. I can barely feel it, but I can feel it better when holding the shifter. I thought it might be the tranny but Idk. I changed the tranny fluid not too long ago and didn't notice any metal shavings or anything to suggest it's going out. So I'm doubting it's that. But I'm not very good at diagnosing issues like this. Thought maybe the drive shaft needed greased again too but I did that like 6 months ago or so. Don't think it's anything suspension wise. Wheel bearings probly needs replaced but I would think that wouldn't cause a vibration only at 1500 rpm. It also does it when just cruising at like 30mph at 1500. But it's most noticeable when taking off slowly. I do have a grinding noise coming from the front engine area but that has been there for quite a while now. Think that is something with the timing or water pump. Still have yet to pull the belts off and see if it's any pulleys. It's not the idler pulley. But I am pretty sire it's the water pump or timing belt pulleys. I am ordering the whole kit to replace all that soon. But again I don't think it is contributing to the vibration. The only other thing I did recently is put in a new high output alternator and big 3 upgrade but don't see how that could affect anything. And my cat is probly no good. I installed the urd o2 simulator a long time ago. Could this cause any long term affects to motor?
Other thoughts are maybe motor mounts. Or torque converter..??

 

I doubt its the torque converter or the engine mounts .
Depending on the year of your truck , you can remove the belts and run the truck "shortly" for diagnostic purposes .
Removing the belts will eliminate all possible issues at the front of the engine .
Proper way to check a universal joint is by removing the driveshaft and this is where I would begin to look . If your feeling vibes on the shifter , there is a good chance one of your universals is done .You cant tell if a universal joint is seized or sticky without removing the shaft .
Removing the driveshaft is a pain in the butt , however it will eliminate that possibilty

 

So how would one determine if the u joints are bad upon removing the drive shaft? I 'jiggled' the shaft last time (before) I removed it to replace the carrier bearing and it didn't budge. But again that was probly 6 months ago. I'll inspect it again. Maybe since my shocks are bad and*clunking on bumps now it may have worn em out more. And I'll browse the book too for inspecting the u joints. But Idk it seems like it would be noticeable period not just in lower rpms.?
And I got a lift at my disposal so driveshaft is fairly easy for me

 

All it takes to create a vibration is one seized universal cup and there are 4 cups within each joint .
With this said , you cant tell if that cup is seized with the driveshaft connected .
Removing the driveshaft and manipulate each universal joint by hand from side to side feeling for tight spots as you go

 

Ah got it. Cool thx man. I saw this done a long time ago. U just refreshed my memory. Thx ima do that and see. Won't get to this till next week. Gonna check the pulleys too just to make sure it's not internal before I order the water pump and timing belt.