accelleration is jerky and friction noise from driveline

[got mph]

hi everyone, first time poster.
untill about a month ago ive never driven or knew anything about a stealth but that was the car i decided on and bought it in florida and trailered it home to Michigan. i love this car. its a 91 twin turbo awd aws.
the seller told me the 1st 2nd synchro was gone and had to be carefully driven which i am doing and looking forward to replacing the 5 speed with the 6 speed used on the later models. ( right , get on with it )
i need help and advice in diagnosing another problem which is as follows
with very light accelleration their is no apperant problem. with moderate accell the feeling and sound of friction felt ( under and rearward ) and jerkyness untill speed levels off. the problem is less severe with higher rpms when accellerating for example 3rd gear to 80mph with heavy accell not as bad as 3rd gear at 60 whith heavy accell.

so is this a clutch slipping or a drive line issue like worn joints or gears somewhere ?

i intend to do all the work my self and appreciate greatly all help.

i built 4 ramps to drive the car onto which i used to change all the fluids
(which where changed after this problem started).

ok, thanks again all