Ok, I've got a 1999 Suburban with 181,000 miles on it. 350 Vortec. On Mon. it started pinging badly. I pulled a code that was #6 cylinder misfire. Replaced the cap, rotor and wires as they were all looking a little beat up. #6 spark plug was wet. I did a compression test on all cylinders. Got about 150 psi across the board, except for #6 and #4. They were both around 30-40 psi. I put a few squirts of oil in the cylinder and the compression stayed the same. So, I'm assuming the rings are fine(no blue smoke out of the exhaust), all I can think is that it's a carboned up valve or valves. I ran some Seafoam through it. Made lots of smoke but still had the rough idle, detonation and the same code. I may run a little more Seafoam through, but, looks like I'll be pulling the heads this weekend. What I'm thinking of doing is getting some new or rebuilt heads, an aluminum intake manifold, water pump and all the little things I come across. Am I barking up the right tree? Looking for some advice on where to go from here. Thanks