It is a 2000 Ram 2500 4x4 with 75000 miles.  I had the trans serviced
with a new filter and fluid flush  at 72000 miles and there was no
debris in the pan.  Once again ,  it doesn't jerk all the time.  Only
after I've driven awhile and the truck is warmed up.

According to the FSM, the OC isn't in use in 3rd. I'm not sure how its in
use in M2, but not in D2 or 3rd, but thats the FSM claim.

But the clarifying point is this: if the OC is operating on the two ranges
(particularly M2) that are fine, its probably doing ok. M2 doesn't have rear
band application, so the OC is on its own, and he has no slippage.

Last, the rear clutch has lower loading in 1st and 2nd ratios, so it'll
hold. Run in 3rd, and the rear clutch starts to slip.

I was thinking that since it jerked in 'D', when just the overrunning clutch
is holding the rear drum, but doesn't slip in manual 1, where the rear band
is helping to hold the rear drum.  Am I confused?

Its not his overrunning clutch, that holds in both manual low and manual
2nd, and his trans is working ok in both of those. However, the overrunning
clutch would aid the rear clutch in holding in both those positions. No
slippage in Reverse indicates that the front clutch and rear band are ok.
Slipping in 3rd would indicate a problem with front clutch or rear clutch,
and we've eliminated the front clutch by the reverse elements being ok.

I'd say its the rear clutch in the main trans housing, or fluid feed to it.
Assuming no codes, and a functional governor solenoid set (didn't see the
year of the trans), its time to look in the pan for debris.

Hmmm....  not good.  Your rear sprag could be worn.  I'm a bit out of my
depth on this one...  any tranny guys reading this??

Okay Tom,  If the truck is in low 1 or low 2 it does not jerk.  It will
not jerk in reverse either.  Only in drive.

Any suggestions?

Dirtclod