Sluggish after startup
 

I have a 2000 blazer 4.3L. No codes or check engine light. After start up my blazer has trouble going over 2000 rpm or 20 mph but after about a quarter mile it starts running normal for the rest of the trip. It revs fine in park or neutral. Sounds fine at idle. And it only happens after i put it in drive and try to go. No loss of power when I slow down or stop. Any ideas?

Shots in the dark here:

Is it that it won't accelerate well until you have driven a 1/4 mile? Or is it that it will accelerate fine up to 2,000 rpm but just not go above that?

Is the condition related to distance driven, the speed driven during that time, or time idling in park or neutral? E.g. Does the motor need to warm up more before it works fine?

Have you checked the transmission fluid level?

It happens as soon as its dropped into gear and I try to drive. The engine will not produce any power. Doesnt feel like its the transmission. Just feels and sounds like the engine. But about 10-20 seconds of driving, it starts going like normal and doesnt happen again until after the engine is shut off.

Well, try checking any of the easy stuff you can think of. E.g. Is the transmission fluid filled?

There is obviously some connection to the transmission; either because the transmission is not working correctly (the torque converter?) it is over burdening the engine or that the amount of power the engine can output is deficient to overcome the small load the transmission puts on it when put into gear.

What is weird is that the symptom goes away after I short drive. This is why I asked about if it was a time or distance thing.

What happens if you leave the truck in gear for some amount of time equivalent to that first driving distance; perhaps revving it while you depress the brake? Will it work fine then?

Ill try some tinkering with it tomorrow and ill check the transmission fluid

Update
 

So since i last posted about this i have yet to figure anything out. I had the catalytic converter replaced and it still does it. Also i dont think its a transmission issue as i found out if i start it up and let it idle for a couple minutes there is no problem. A buddy of mine suggested maybe its losing fuel pressure when its shut off. I has had a new fuel pump put in years ago before i bought it. Maybe faulty install or something.

Even if it's leaking down fuel pressure while it's off, it doesn't take but a second or two for the pump to pressurize the lines.

Either way, you might try checking the fuel pressure when it's having the issue, to at least see what's going on