2000 Cougar eating tires and loosing power

[IZ1111]

Hello, I have been driving a 2000 cougar recently for the past months and its been abused, badly. I've just made some tune ups to everything from oil change, sparks, cleaned MAF sensor and all filters changed. (But where the heck is the PCV valve on this thing?). But my problems is that I only can get a top speed of 65mph. Its like it won't jump to the next gear when I reach this speed. Also hesitates accelation when going up around 40-50mph. Could this be a transmmition problem? It has been serviced already one time before. But here is the worst part, it eats up tires every month, The back two tires. I think the rear shocks are defective because the tires scrape the shocks and show rings behind it just threading away until you get a flat. Was is a bad year for cougar in 2000?