1996 suburban 5.7l engine miss - low rpm

I have a 1996 suburban with 5.7l engine. It has 118,000 miles on it. I had to replace the intake manifold gasket approximately 18,000 miles ago. I did the job myself. The engine seemed to have a hesitation at approximately 50 miles per hour with low rpm and light throttle pressure. There was no problem before the intake gasket repair. With heavy throttle pressure the engine seems to run fine. I have replaced the air filter to a high flow / cold air filter, plugs, wires, fuel filter, pcv, etc. I have always supected the distributor but have read that the computer controls the timing. I have followed a procedure I found in alldata to install the distributor correctly. I do not have a check engine light on. I have a scanner / code reader which shows no trouble codes. The scanner shows me live data from the data connection and I have found one reading troubling. The ignition advance shows -22.5 degrees. I have read several posts with similar problems ( hesitation not timing ). My code reader does not show cam retard offset and I don't under stand what that is. Is the timing reading I'm getting consistent with cam retard offset or some other condition causing the computer to retard the timing. I'm under the impression that only an automotive shop can set cam retard. Any help on the subject would be greatly appreciated. I have been scratching my head for over a year on this without biting the bullet and taking the burb to the dealership.