Ok.....so in the past couple weeks I have had some trouble with my '99 Silverado 5.3. I thought I had fixed it last wednesday. It has been running fine since then. Here's the history of the past couple weeks -Turns over but wont start. P0108 code, I replace MAP sensor, Still wont start -Fuel pressure around 52psi key on/engine off. -I replace the fuel filter, and get it running with starting fluid. Fuel pressure around the same when running. Idles but runs rough. -Clamp return fuel line and pull vac line off regulator to get 90psi. I replace fuel pressure regulator. Starts with starting fluid and when its warm, but no cold start -Replace fuel pump and get it to start cold, but runs rough. I get code for multiple misfires. -Replace all plugs and wires. Runs Great! And thats where I left off........until tonight Today I go to start it, its cold. I start it and notice a "chattering" noise coming from down by the fuel filter/fuel line. I drive for about 30 minutes then let it sit for about 8 hours. It gets cold, down in the 20's. I go to start it and I get the exact same thing that happened at the very beginning......Turns over, wont start, CEL Code for MAP sensor....UGH!!! So its stuck at my parents house, was there for a christmas gathering. Im in there the whole time telling my parents "Oh yeah I finally fixed the truck, running great now".....LOL Luckily they have a garage and its parked right in front of it. Depending on the responses I get from this thread, the first thing I plan to do is inspect every inch of fuel line that I can. I do recall the fuel filter was a bit difficult to remove, little bit rusted and I could have tweaked the line somewhere, but from what I inspected I did not see anything. What a fiasco. - - - Updated - - - What other sensors would cause this type of condition?