89' stang problems

[mustang4life121687]

i have an 89 stang, wit a 4 banger motor n i recently had 2 replaced the tranny, now i got a 86 tranny in it, n i had to make a coustom drive shaft , and it was suposed to come out of a chavey and i took the old ends off my 89 drive shaft n put on it, and it run fine for 2 days, and then strated to slip and i had to rev. it up to about 3 1/2 rpms, and it finaly took off in and when i droped below 15 mph. i had to rev it again, and i just put a new filter in today and it drove 4 like 20 min, now it wont go into ne gear other then reverse, can ne 1 tell me what might be wrong wit it?[/COLOR]