Volvo Repair: Automatic Transmissions, drive shaft center, automatic transmissions

Question
I have a 1988 740 GLE, with 250,000 miles, and the transmission stops working after the temperature reaches X, does not overheat, works after cooling down, shifts hard when cold.  Probable diagnosis? Did change the filters and have done basic maintenance to it, but no professional repairs done to correct problem.  Can I install a 1987 Aisan Warner AW71 with and intergrated torque unit, into the 1988 which has a ZF4HP?  

Answer
it can be done, but you need to swap alot of stuff over the zf is a very bad transmission. you will need the shifter and crossmemeber and probably a few more things. i have not done it, but i have heard of others sucessfully doing it. possibly a drive shaft? center console? but if your swapping, it should all be available.