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