I have a 99 Jimmy, 4.3 V6, 2WD, auto, 159k miles, runs like crap. CEL gives a multiple missfire code. Changed the cap, rotor, wires, and plugs. No improvement. Thinking it may have jumped time, ( the ex wife cranked it up and floored it in a drunken rage), I started checking for the signs. I lined up the timing marks (both of them) on the harmonic balancer, and the distributor was off the #6 cast into it by about 20 degrees. So I double checked with the old school method. I pulled #1 plug, and with a plastic tube from a can of WD40, I felt for the piston to come all the way up to TDC. At this point the distributor lined up with the #6 cast into it perfectly, but the timing marks on the harmonic balancer are off by 20 degrees. Is that normal? Should I assume it has jumped time since the timing marks and distributor did not line up, regardless of where the piston is?