Lots of great info here. I have a bone stock 98.5 (auto) and my fuel mileage has decreased and also have noticed a loss in power. My fuel pressure is 15psi at idle and 12+ at 70mph, while pulling a trailer (12,000lbs) its at 12 psi also. I have replaced the IAT and MAP sensors and this is my second lift pump the truck has 165,000 miles on it and smokes a little while pulling a trailer up hills. Any advice or help would be appreciated.

 

As far as the engine goes, check/replace the filters. Has it always smoked? One guess would be a full air filter. Where are your fuel psi reading comming from? But depending on how much smoke were talkin id be checkin the Air filter. But then you said its only up hill( just noticed that one) So air filter could be fine.

Another thing you just might want to check is Tranny, when was the last time that was serviced? A lot of times people dont think of that as being a reason for "low power" They are making the power just not getting it tot he ground

 

VP might be getting tired....

 

Thanks Kingofdodge7131 and Hohn. As far as the transmission goes, all I have done is change the filters and fluid on a regular basis, I haven't had the bands adjusted as of yet (currently looking for good transmission shop locally) but I will get that done asap. I also run Lucas fuel additive regularly and it has crossed my mind the VP is going out. I tapped into the top of my fuel filter canister for my fuel pressure readings. It gives a white puff of smoke when you start it, but usually mainly when pulling a trailer, especially on hills. I have changed all of my filters also.