1990 TBI timing question.

[1990GMCVan]

I have a 5.7L in my G3500 van that I use for towing my trailer. Recently I had a coil meltdown. the carbon contact in the distributer cap broke and the coil arced from the terminal in the cap to the rotor button until the coil died. Now with the new coil, cap and rotor button, distributor(pickup coil was also trashed) the truck still does not run right. At closed throttle the old OTC scanner I have tells me I have 1.0 volts coming in from the MAP sensor which loosely translates to 8 inches of vacuum. I t'ed off the vacuum line at the sensor and there was between 19 and 20 inches of vacuum at the MAP while the OTC scanner read 1.0 volts (8 inches of vacuum). The TPS when closed is at .70 volts. When I open the throttle just a little, the MAP voltage indicates true manifold vacuum. The timing at idle is low but when the throttle is opened a little it jumps app 20 degrees. When the knock sensor picks up a knock the timing snaps back down 20 degrees or so until the knock stops (brakes locked up full throttle). According to the OTC Scanner the other sensors are giving reasonable indications but there is still a flat spot in the acceleration when going down the street. The timing is now set at approximately 20 degrees advanced with the timing connector disconnected. Before the failure the MAP would give a true manifold vacuum indication. I don't know how the timing performed, is it supposed to snap on and off like that instead of tracking the engines RPM. HELP