2002,My car won’t go past 35mph

Hi. My car will not shift to third gear n it wont go pass 35-40 mph without the rpm going higher. I got a rebuilt tranny about 11 months ago n the car was running great for about 4 months. I went up a hill n stepped on the gas n sped up to 55 mph n then the problem came back that instant. I was unable to go into 3rd gear again n couldnt go pass 35-40 mph. The rpm would go higher but my speed didnt want to go faster. The oil meter would go higher when i stepped on the gas n would go back down when i let go. I had someone look at it n tried to find the problem but no progress. The head gaskets h