After chasing a bunch of little problems, I've finally got my car running well . . . on 91 octane premium. It's now got: 170lph pump New fuel filter Adjustable fuel pressure regulator set 36psi (vacuum off) New cap/rotor & 8mm performance wires Timing at 10 degrees Was still pinging under light load (70mph up hill in cruise) and went lean over 4000rpm so I cleaned the MAF, cleared the codes and tried again. Bingo, problem solved. Smooth as silk and pulls very nicely to 5500+. So, as the manual says 87 octane regular, I put in a tank. I immediately got some low load pinging back (nothing in cruise at 70mph but as soon as I hit a steeper hill, it gives a light rattle). I've read several forum threads about the computer in '94-'95 5.0 Mustangs having too much part load advance for 87 regular but I want to get some experienced opinions. I've got some 5.0L experience with my cousin's cars but they're all Foxes, so don't have the 3-D programming that the SN95 has and they were running 12-16 degrees base timing with no problems that I know of. I'm going to dump in a tank of 89 next to see what happens but I commute 230 miles to/from work three days a week so burning fuel that's 20% more expensive adds up. It'd be nice not to have to run 91 all the time. I'm planning on getting into the computer but was going to wait until I put my heads, intake and cam in. Maybe it's worth doing now and backing off on the part-load advance. WOT and/or 3000rpm up doesn't seem to have a problem, it seems like it's 1/2 throttle and below and below 2800ish rpm, hence my thought that it's an ignition advance issue. The previous issue affected WOT and threw 181/189 codes, so it was clearly a lean issue. This is my first SN95, and it's teaching me a whole lot about the last 5.0L! It's kinda fun but, for a car I rely on every day, I'd rather not spend every morning listening to the engine for nearly 2 hrs listening for pre-ignition rattle.