Need help guys...

Alright, so as most of you know i just bought a 97 mustang gt. Automatic, the tranny slips bad in first gear. Im getting it rebuilt. Now, im looking for a shift kit. I really dont know anything about transmissions and shift kits. Can you guys recommend a good brand that will hold up and wont break the bank.

Any info would be great!
Thanks!

It just doesnt grab in 1st gear. After i rev it up to about 3500 it grabs right into second and then it shifts fine through all the other gears. Ive talked to numerous transmission specialists and they all say the same thing "something is wrong with the forward clutches".