If your engine is at 6000 rpm at 80, it has downshifted properly, and should accelerate pretty well. Though you MAY have transmission problems, a thorough go-over of the engine would be where I'd start. Fuel system, per yaser, air filter, check for vacuum leaks, pull spark plugs and inspect (you could take a pic and post it here, and get decent feedback) while the plugs are out, do a compression check. If that gives no joy, I'd get a GOOD scan tool check, as Scotty shows on YT. Then check the transmission. If you watch Scotty, you know that his usual response to transmission problems is put in a new one or junk the car - very little that you can fix/get fixed for what an 02 car is worth.

Look you don't even have 200hp If you going 80 which is already really fast its not gonna take off like a rocket. You could have 200hp gocart and if you going 80 you might gain a little bit of speed but its not gonna blow your hair back. The only kind of cars that can be going that fast and still have wicked acceleration are race cars with insane horsepower. And its a 2002 there no way it still has 197 hp after all these years...  

if you are sure that it used to accelerate better before, than the transmission is not delivering the 6000rpms from the engine to the wheels anymore. I guess your automatic transmission is wearing out, the time has come to baby it if you want it to hold up much longer. I generally advise against purchasing anything with used automatic transmissions because of it.

Check the fuel system: Change the fuel filter and then pressure test the fuel pump. Odds are that this solves the issue.