4L80E High RPMs?

[Gordonr1973]

Hi all;

just about to do some trouble shooting on my transmission.

Yesterday was the first time I took the truck (LQ9 motor with new Comp Cam) out for a drive on the freeway.

I bought the tranny as a pullout from a cargo van with about 20,000 miles on it.

I didn't build the tranny up at all, other than to change its filter and fluid.

On the freeway yesterday it seemed not to want to shift out of 3rd to fourth??

I was driving about 45 to 50 mph and the tach was showing inbetween 3k to 4k RPM.

Any suggestions on what to check for? I thought it might be a case of low Auto trans fluid but I checked it & that seems to be fine.

Could this be something corrected by a new PCM tune (which I haven't had the final tune done yet) of the shift points?

Thanks!