1997 Challenger 1800 - has been running like a top! - until yesterday

*speed #'s are according to speedometer not actual speeds
I'm cruising @ about 5k ---> 40mph* --->6k (50mph*) ----->7200k(60mph*)(WOT)
THEN - It feels like when a tranny slips on a car -and I can't get above 40mph* even at WOT!
Now I have to run @ 4k just to start moving!
Are my impellers - clogged? Broken? I'm at a loss here!
anyone bueller?
