88 Thunderbird any tips for new owner?

My 1988 ford thunderbird wont go in overdrive gear, it goes to shift into next gear after 3rd and just goes into neutral, i have to slow down for it to go back into gear. Is that the transmission speed sensor?
If the transmission in an AOD it sounds like your OD input shaft could be broken. The first version OD that Ford built was the AOD. An all mechanical 4spd automatic transmission that used 2 input shafts in order to achieve lockup in OD. When the trans shifted to OD it actually bypasses the torque converter and uses the second smaller input shaft that is directly coupled to the flexplate. In order to make this diagnosis you would have to pull the trans to inspect.
Take care
I would pull the dipstick first and make sure you're not low on transmission fluid. Look at the color of the fluid and smell it. Good fluid will be red. Bad fluid will be tarnished or dirty reddish brown and it'll smell burnt. If it does drop the transmission pan and change the screen filter and fluid. If possible unhook the transmission line going to the bottom of the radiator and top line going to the trans and use air to flush all the old fluid out of the lines and radiator. Refill with new fluid after lines and screen and pan is put back on