I have a 96 Blazer with a 4.3L V6 with CSEFI - 172,000 miles. Within the last year or so I've done the following:

Replaced distributor, cap, rotor, wires, plugs, coil, pcv, crank sensor, O2 sensor on the driver's side exh manifold, fuel pump, and inline fuel filter under driver's side of the vehicle.

I've also recently cleaned the EGR and IAC valves.

The vehicle runs fine except for an intermittent miss at idle under load, a few misses when initially taking off from a stop, and when on the highway under acceleration for passing, climbing a hill, etc.

It has recently set codes for a random engine misfire, O2 sensor - bank 1 sensor 3, and MAF low voltage. Watched everything with a scanner and nothing looked out of place, so I'm thinking the codes are setting as a result of this random "miss" - not due to actual issues with those sensors.

I haven't checked the timing, but that's my next step. With the scanner hooked up it showed between 17 and 22 degrees of spark advance (is this normal?). I had to take it to a shop at one point where they replaced the crank sensor and told me the distributor was off a tooth. I'm worried they made an error when getting everything back together and got the timing off. How much will the PCM be able to correct for if the timing isn't quite right or is off a tooth?

I've also seen where some say there is an issue with these engines having valves stick from time to time. I have about 172,000 miles on this one. As long as I've had it, it has occasionally set a code when downshifting to pass on the highway - but the code goes away after a few days of driving in town. I've seen on the web where this condition is related to valves sticking in a communication from GM.

Another thing I think I've noticed is that it doesn't have this problem when cold. Once it warms up is when the issue rears its ugly head. Maybe an open loop vs. closed loop thing?

I know this is a lot, but I'm running out of options and need to get this thing running right (daughter's car).

Thanks