I've got a 1991 chevy silverado 1500 that'* got 1999 heads on it, and it'* throwing code 34 with is indicating high vacuum for the MAP Sensor, problem is I've changed the MAP Sensor twice, no air leaks anywhere, and I feel like I might have something to do with the lack of EGR maybe? 1991 Egnines had one and 1999'* did not, so i don't know if that'* part of it? All help is appreciated looking for a work around or a fix. Thanks.

Did you do any testing? What does the scan tool show at KOEO? idle? 4000 rpm?
I have the factory info for it if you would like something.

Have scanned it with KOEO, but idles around 1200, idle isnt rought or anything, but she'll die just idling, and ill lose power running down the road around 55-ish

I was looking for numbers.
Did this start right after the heads were done?

I'm not sure I bought it after the heads were done I've had it maybe 3 months and it'* done it the whole time

What is the MAP value with koeo?

It'* about 1-1.2 Volts. That'* what your asking correct?

I'll need to get my info pc fired up and see what the value should be at your altitude. What is the altitude there?

4150 ft

That reading is way to low which corresponds with the code set. Here'* the info on it.