1989 Chevy Silverado timing change

Greetings-new question I partially rebuilt a 1992 4.3 that was in my 89 chevy pu. New valves #1 cyl,reset all other valves, honed cyls, put new standard rings in, new standard bearings, all torqued to specs. set up motor- new plugs, wires, cap/rotor, tstat,egr valve, reset valves to specs, set #1 tdc for distributor, new fuel filter. have not set in the rings as I can't motor to run right. Timing is set 0 degrees with tan wire disconnected- plug wire in timing stays at 0 running at idle- mech said it should be 6-8 degrees at idle. rev up motor and it stumbles ( lots of fuel tbi spraying well) then timing may jump up to 8 and stays there unless throttle is eased a bit off, it then drops to 0 again. vacumn is 15-17 in at lowest port on tbi ( no port on manifold to use) drops to 0+- on rev-goes to 20-22 off rev has twitch at 15 in at idle. PVC has vacumn and working,EGR ok, MAP has vacumn, coil and distrib wires and other wires tight. did throw codes after I did check- were 33,44 both from MAP chech and timing tan wire. cleared codes no more new. cold start runs and almost dies, catches and revs up- does this about 3-4 times till warmed up, starts ok when hot. what isn't telling what to do, or what isn't doing what its told