Tranny - won't shift into passing gear
 

This question is for my brothers 2002 GP GT. He is having trouble with his tranny not wanting to shift into passing grear (it slips), other than that it is as smooth as can be. He recently did some maintenance on his engine and the next day it acted up on him. My question is, what controls the passing gear shift down? Is it electronic, vacuum, etc., or is the tranny starting to go? We are wondering if he knocked an electrical/vacuum line loose, or something. It seem like an untimely coincedence. We're looking for the best way to attack this thing.

oh, and he said his check engine light blinks three times when it slips.

Have the car scanned to see if any codes are coming up.

What did he do to the car just before it started. Check the fluid level and color. How many miles on the car. Give everything a good close look where he was working. Make sure nothing is loose or off.