[Shifty12]

I installed a TRANSGO SK®4-SL FORD C-4 TRANS TRANSMISSION SHIFT KIT in my 1967 Mustang 289 with the C4. All I did was drop the valve body and replace the springs with the new ones that came with the kit. After driving the car 1st and 2nd gear work great, but for some reason the trans will not stay in 3rd gear, it keeps slipping form 3rd to 2nd... Any ideas on this PLEASE HELP!!!! I disconected the kick down and, it got a little better (didnt slip as bad) but still wont stay in 3rd gear once you press the gas.

[PaulS]

Check to make sure the vacuum modulator line is connected tightly. Re-connect your kick-down because it really doesn't have much affect on part throttle shift points.
If the modulator is connected properly then you problem could be the governor or improper installation of the kit.
To be absolutely frank, you should have installed the 47-2 reprogramming kit instead, in my opinion.

[The Greek]

I would review the instructions. Sounds like you missed something. Did you use a torque wrench on the valve body? The torque being correct is critical.