Please Help!!

Hi,
I own a 1989 4x4 Chevrolet Blazer with a 4.3L V6. It has 218K miles but has been well taken care of! It stumbles and wants to stall upon acceleration and the idle fluctuates a lot. I've checked the timing and its ok. I've replaced the spark plugs, wires, cap, rotor, air filter, fuel injectors, and fuel filter. Fuel pressure is Ok... and EGR is functioning properly. I thought it might be a plugged converter... So i drilled two 3/8" holes straight up through the bottom of it... (I dont know if this accomplished anything!) The problem seems to get better once the vehicles been running for some time. The Service Engine light works but is not on. I recently checked a spark plug again and it appeared white signaling to me a lean mixture... I'm really lost on where to go and what to do next!?! If anyone can help me I would greatly appreciate it! Thank you so much
Matt

I think you need to be looking for a vacuum leak. Listen for hissing or whistling. Try spraying some carb cleaner on vacuum hoses, intake gask., throttle body base. etc. . If you get an rpm increase, you've probably found the leak. Look at the pcv hose. They can get soft and tend to leak on the underside where you can't see it. When your vehicle gets warmed up, it needs less gas and more air, hence it runs better.