My son's '90 525 iA is demonstrating a shifting problem. When cold, if doesn't want to shift out of first. After a few minutes of warm up, if you back off the throttle at the point it should shift, it will go into 2nd. Once it completely warms up, it seems to work fine.

I checked fluid level, if anything, it's a little high. The tranny was rebuilt about 10K ago. Could it be a linkage problem?

Thanks in advance