Transmission and Oil Pressure is my main concern

What is your question?

My 2000 (3.8L V6) Chevrolet Camaro runs fine, unless im on a long drive (one hour or more at highway speeds). Once i have been riding at highway speeds for an hour or so, and come to a stop light, when the tranny changes from first to second gear it jerks forward really hard. I have changed tranny fluid and filter and I am hoping for a little bit of advice. Also,(un related) My oil pressure in my car is fluctuating by as much as 50 PSI. its never flucuation low, but always high, so im not overly concened, but i am worried i may be causing premeature damage to my oil pump. I also changed my radiator fluid and the radiatior had a bunch of what looked like off white play-dough stuck to the radiator dipstick and the fluid that was in there was darker than it should have been. Someone told me that I maybe leaking oil into the rediator...does that sounds abuot right to you and could that be the reason my oil pressure is jumping so bad??? Thank You!!!