2000 Losing Power While Driving
 

Hello all, noob to the forum! Lots of experience with performance/modifications/racing - none in modern Northstar-powered Cadillacs.
This is my mother's 2000 Deville

She was driving the other day, and out of nowhere the car started losing power (mph dropping despite constant throttle).
Then, just as suddenly, it came back to normal.
The car/trans clunked when it came back to life.

Couple miles later it repeated the problem, same symptoms - slowing down, then a clunk as it came back to normal.

I couldn't get it to repeat the problem. No codes.

My first thought is fuel filter, but I see alot of posts re: the crank sensor having problems. No stalling at this point, and the car was running and she's not describing a miss, but simply the car slowing down even though her foot was on the accel.

Car has had regular maintenance - but none in the last 2 years. It burns oil (gee, shock, lol) and smells of coolant, butshe already keeps those levels checked/full. She doesn't think the filter has ever been changed.

Anyone had any experience with this type of problem? Thanks for any ideas you guys have.