94 jetta III tranmission problems

When car aproaches 40mph but instead of shifting into 3rd, it just revs higher and higher, until around 55mph, then it bangs into third, I have had it at the mechanics 3 times, last time it took 2 1/2 weeks and was still not repaired. mech assured me that trans was ok. it's an auto. any advice would be helpful, I am really depressed.

check the tranny mount sounds kinda screwy but it might be just that

thanks for the tip, the mechanic had changed both mounts, which made me suspicious, because those bolts are fastened to the frame, i'm wondering if the trans had been worked on before. he claimed they were cracked? it acts funny in colder weather it seems.

If it's a harsh shift only into 4th then it's probably a shift solenoid or shift valve problem or broken wiring (all inside transmission). You may be able to get fault codes from your trans control module. Find the diagnostic link beside the ashtray (pull tray out, slide cover left) and jumper pin #4 (top row fourth from left) & pin #15 (bottom row second from right) for 2 seconds with ignition already on. The check engine light will flash a series of four digit codes. 4444 is end of codes.