Ok, I have a Dodge Dakota, 2001. 4.7 L. V8 magnum. 5 Speed manual trans.
Symptoms may or may not be related but all occurred at the same time.
Very strong exhaust fumes in environmental system. If you defrost windows, you have to open doors to clear air.
Oil pressure gauge went from just above "1/4" to just under "3/4" mark.
Loss of power on hills.
Hideous loss of gas mileage, went from 22 highway to 10

Unit idles fine. seems to run normally on flats, since power is not needed.
Any ideas?

In the shop we use a smoke machine to find leaks in exhaust systems and evaporative fuel systems. You've picked up some kind of nasty exhaust leak and I imagine it's upstream of an O2 sensor so that the engine is fooled into believing the engine is running lean when it's actually running rich. The exhaust leak can be ferreted out with the smoke machine (find some shop that has one) and when you fix that you'll probably fix the other. That's a guess, which is quite tough from here to there. Don't see any TSBs on that truck and that problem.