'03 5.3L Silverado

My truck recently started having problems while pulling a trailer back from the Dunes. The check engine light came on but someone (who will remain nameless) decided to clear out the code to see if it was a real problem. Well, it's a real problem and now the code won't come back.
What it's doing -
This normally happens when the engine is warmer and can happen either at lower speeds or fairly high (75-80) speeds. It's almost like the tranny slips but then catches itself. The feeling is like when the governor engages if you ever felt that. And when it starts to happen it'll happen a bunch of times in a row. I don't think it's a trans slip but wasn't sure if maybe a solenoid is not working? I've noticed it happen also while downshifting while in cruise control. It's a cross between it feeling like when it goes into overdrive and when the governor kicks in. That's the best description I can come up with. Also, there is a high pitched whine noise as it's going up to shift. That started around the time this all happened. It actually isn't as loud now as it was when this first started. I have about 180K on the truck and I guess maybe I could put a trailer back on it to try and get the light to come back on but am worried that it'll damage the truck more...Any ideas? Thanks