Just got my 86 D150 Back on the road been sitting for over a year..Tried it out today and ran pretty good but i noticed that it had a bad shutter when pulling out in 1st and reverse..Has the A/833 Trans 3sp with O/D ..Think it may have something on the clutch surface from sitting so long?I may drive it some more tomm see if it improves any..Thanks

Sitting too long can cause rust to build up on the flywheel, if driven regularly the clutch wipes it out before it forms... but sitting too long the clutch disk might have some crud on it...

There can be other things that can cause this issue:

Rear seal leak getting oil slung onto the flywheel/clutch disk.

Clutch linkage not adjusted quite right.

Flywheel surface not true/flat.

Clutch disk work out (I had one shudder, then "stick" in my mom's valiant, found that the disk was worn so bad that I actually cracked a section out of the disk).

I have had it happen after I lost the rear transmission to crossmember mounting bolts... which if the rear bushing was rotten might happen, but usually you might hear a loud "thump" as the tailshaft and slip yoke hit the floor pan....

Fun with old cars.