transmission rebuilt , new problem on 2000 Ford F-350 Super Duty

Just had transmission rebuilt, got the truck back, runs great in forward, but when put in reverse rpm drops down to 500 and sputters then jumps to 900 then falls back down to 700 rpm. With trailer hitched, truck sputters even worse. any ideas?

Bring it back there must be some kind of warranty on this transmission repair
1 more answer
I am having the same problem, trans shop went through trans twice, I am looking for electrical problem, you might ck altenator be sure it is charging like it should. If you find problem I would be interested.