So every thing works great, but the engine has a problem of not shifting out of second and into third. You can rev it up to 5g rpm and it'll jump into third and afterward's run amazingly, until it shifts down. Could this be a vacuum leak somewhere in the engine or solely a transmission problem?

 

Hi! Not sure this is related or not, but did you adjust your kickdown cable?

 

Bingo. First place to start. It's free, it's easy, and it just might cure the problem. If not, well, nothing lost.

https://www.youtube.com/results?sear...ickdown+cable+

You might need some penetrating oil or WD-40 on the adjuster button. I had to play with mine for about 10 minutes to get it operating freely. Then the actual adjustment was about 30 seconds.

 

That's what Mark is suggesting above. But, it's not a "kickdown" cable. It's a throttle valve cable.

Shifting is controlled by the tCU sending signals to the transmission solenoids based on input from the vehicle speed sensor and most importantly the throttle position sensor.