Prior to installing my turbo last week, I could occaissonally feel a vibration when I accelerated hard, now I can feel it even more and especially when I am pulling my trailer. I use this truck to pull a 16' trailer that is equipped with a large smoker mounted and am headed out Thursday to another competition about 150 miles away. I am concerned about what is going on with the motor but I guess I need to run it till it breaks to know what is wrong unless someone has an idea. This is not the original motor but I am the second owner and the original owner was my wife's grandfather who was a farmer so it has not been abused. Anybody got any ideas? I know the "vibration" question is a little dumb sounding but I have been around equipment my whole life and something is not right about what I am feeling and hearing.
Thanks for your comments and suggestions.

U joint? Carrier bearing for the driveshaft? Bearings in the rear end?

My hum/vibration at 45mph in 3rd was due to a worn ujoint.
You could also inspect the harmonic balancer on the front for cracked rubber.

i had a bad vibration and howling with my carrier bearing on the driveshaft. it actually blew apart on the highway after howling for almost 30,000 miles. Don't get stuck in that situtation, trust me it's not fun.

My truck does not have a carrier bearing on the drive shaft, I have replaced everything in the rearend when I installed the 4.88 gears and all new u-joints from front to rear. If I am remembering correctly, this started when I had the front-end worked on. I had a local 4X4 shop relace the front axle bearings, install manual hubs, and one tie-rod. Could any of these be the culprit? Could it be something in the transfer case? I rebuilt it myself so there is a possibility of an error there but it has been months since it was repaired.

make sure both hubs turn off for you. i have auto hubs and one was gettin shy on grease and it stuck on and when one axle turns it vibrates like a bugger. greased her up and it worked like a champ again. but then it started it again. so i backed up and it quit afterwards. love my autohubs but that deal is getting rediculous

you've got 6 inch lift. it can eat ujoints pretty quick, so inspect em. its easy for one to go dry and make noise .being an 83, the transfer case should be part time and turning nothing in the front end unless a hub is locked. i had a growl in the front once, a spider jammed or broke and it broke the hub inside, made it growl on tight corners and fought the steering box

What trany you got? I have a 700R4 and when the lockup converter started to go out it shuddered under acceleration.

I have the 700r4 and have seen all kinds of folks talking about their torque converters and having special lock-up styles. I am very ignorant on torque converters. I had the transmission rebuilt a few months ago but have no idea if they put a new one in or just my old one. Guess I should have ask. Got under the truck last night and the pinion nut had slack in it, I am pretty sure that could have been my problem. Won't know for sure till tonight.
Thanks for the ideas!

Just to give you an idea of what happens when a lock up goes bad, my running temp went from 120-130 in summer to the gauge pegged past 250! When that lock up slips big heat. Run a lock up tranny out of lock up for a while and it gets around 200- 220. My suggestion put in a gauge whether the trans is going out or not.