OK, so the 1999 K1500 Suburban has roughly 180K miles on it. I've posted here in the past about my upgrades and maintenance, but I'll give a quick recap: New u-joints, trans filter and fluid, rear diff gasket and gear oil, new plugs, wires, dist cap/rotor, K&N intake kit, tires/wheels, work done on windows and door handles... and maybe a few little things I'm forgetting. I've run Seafoam and some other fuel injector cleaners through the truck over the last six months of ownership. I've done other cleaning and tweaking. I've had a fuel filter waiting to go in. I just haven't done it yet. It has always felt like it was bogging down some while going up hill. You have to back off on the gas some. After running injector cleaner through a tank of gas, it usually feels more powerful at WOT. It feels much more aggressive. But, after another regular tank or two, that power disappears. Now, we are up to this week: I live in Dallas and took it down to Austin and back on Tuesday. It's about 400 miles roundtrip. It did really well the whole way and felt strong! Then I had to travel to Lubbock on Thursday, which is about 800-900 miles roundtrip. It did well on the way there, but started acting up on the way back. About an hour into the trip, it started losing power pretty bad. Anything except for a very light feather-touch on the pedal while going up a hill would make it feel like it was about to turn to dust and die. The road was 75 mph, but I could only get it up to 45 mph up hill, then going back down, it would easily gain speed and get up to 65 or 70. It was like it had zero torque, but still had some HP. Then, right before I found a gas station, I heard a loud pop, like a backfire through the throttle body. I pulled off, thinking it was one of three things: a.) bad gas, water in the gas, etc. b.) failing injectors. c.) failing fuel pump and/or regulator. I bought some lucas injector cleaner and put in the best gas they had, hoping it had some decent additives to counteract any bad gas issues. While at the stop, I checked and filled the oil, noticed that the intake had popped off the throttle body and reattached the K&N intake. I looked over the engine, and everything else looked normal. I got back on the highway and it was running a bit better, then better, then fine. It drove fine for the next several hours and then the problem repeated itself about a hour outside of Dallas... can barely make it up hills, very weak, etc. This time, I heard two pops under the hood and again the filter kit had been pushed off the throttle body. Let the truck sit for a few minutes, then drove the rest of the way home with it feeling a bit sick, but able to do highway speeds again. The truck feels like it loses all torque going uphill, even shallow hills, but can easily gain speed without much effort going down hills, even shallow ones. It just bogs down bad if you try to give it any gas. So, what are your thoughts? I am thinking of picking up a gauge to check the fuel pressure under the hood. I will pop in the new filter. What else should I do?