s10 zr2 slipping transmission

[litlred]

New to this site, and really impressed with the helpfullness and professionalism of folks here!

A few weeks ago our 1999 s10 chevy began having its 'service engine soon' light on. We keep it regularly serviced, and decided to have the transmission fluid & filter changed. Our mechanic did so...fluid was in good condition...relatively clean, etc. No problems.

Light continued to stay on a couple more days. Once truck runs awhile and is shut off for a few minutes, the light would go out. After 3 days, the light stayed off and there was no hesitation on starting out. Everything was peachy.

(a week later) Now there is a hesitation starting off in 1st (automatic trans)...needs higher rpm to get vehicle moving. Reverse is fine. Once on the road, shifting is quiet and smooth with no problems.

Shutting it off no longer solves the problem, either.

Took it to Auto Zone to have them check with their computer...the man couldn't get it to work and says there is no power to the port. We can't get an error code from the computer.

Is there anyone who might have a suggestion as to what is going on and where to start looking for problems?

Sure do appreciate you fine folks...thanks in advance!