thunderbird trans

I have a 95 thunderbird 4.6l. when doin city drivin my trans will only get up to bout 35mph and after that wont shift any higher and the rpms just go up. But if i gun the engine right off the start has no problem shiftin to higher gears but as soon as i take my foot off the gas the trans wont let me go faster and the rpm go up any help would be greatly appreciated.

Welcome to the forum slipknot1488777. I would first flush out the transmission. Some people in this forum swear by a product called Sea Foam. You put it in and drive for a while and then drain the transmission and install new fluid. Be sure to drain the torque converter at the same time and install a new transmission filter. To drain the torque converter you remove the inspection cover at the bottom front of the bell housing. You may have to spin the engine over a few times before you see the plug you have to remove.