I have a th350 that slipps from 2nd to 3rd only under wot. It takes it a second or two to go to third and the motor just revs for a second the it will slowly go in. It never happens under normal driving conditions and 1st to 2nd seems fine. Anyone know were to start? fluid is fine.

Sounds like your direct clutch is affected by a leaky seal somewhere which will eventually lead to a direct clutch failure. Keep checking your oil. The more this happens, the darker and stinkier your oil will become. I'd recommend putting some pressure gauges on it to see if it is a leaky seal. Most likely you're headed for a rebuild.