New Chevy 4.3L Has Misfire --Please Help--

[Rudyfastcat]

opcorn: I have a 1992 Chevy C1500 with a 4.3L TBI and 5 speed manual trans. .
I just recently had a new(rebuilt) 4.3 installed and now I have this mystery misfire .
When I picked-up my truck from my mechanic and noticed the miss & he told me to give the engine 500-700 miles (break-in) . Well here it is 2 weeks & 715 miles later and nothing has changed and I will be taking my truck back for that after break-in check up .
Does anyone have any first hand experience with this type of problem and is there maybe something else I missed ?(maybe valve adjustment is needed?)
FYI - Over the past 2 weeks I have replaced the plugs, wires, engine oil+ filter, cap & coil . I also rebuilt the TBI (includes replacing fuel pressure regulator, TPI sensor & brand new TBI injectors) and still no change . I have also checked all grounds and all is good.

[GMMerlin]

IMHO your mechanic should have investigated what was causing the misfire before returning the truck to you.
It sounds like an engine mechanical issue (I would start with a compession test first)
You shouldn't have to tell your mechanic anything..if he was any good, he could figure it out on his own.