p.s. your timing is 8-10 degrees BTDC for the 1990 5.0

 

I'm not sure about Chevys but I'm my brothers Mercedes same problem. He just disconnected the o2 sensor and it ran 10x better. So he replaced it. I tried that for my problem too, but no help.

 

Is it 8-10 degrees at idle?

 

yes, at idle.
Im not a believer in unplugging an O2 sensor for troubleshooting. a proper operating sensor uses voltage. this voltage changes from .001 to .900 constantly. as the voltage changes it is telling the pcm to adjust air/fuel. so, as an example if your sensor is .000v then unplugging it will not change the "signal" to the pcm. In My experience ive found the best way to test an 02 sensor is to use a scanner that will give you a live data stream while the engine is running, from there you can see the voltage changing on your sensors. autozone has a scanner that they will loan, or they will scan it for you in the parking lot for free assuming you can get the vehicle to them.

 

In these older cars the O2 sensor doesnt do much. This is the second generation catalytic converters.

I am not sure what the problem is, does it loose ***** climbing a hill? Or does it stall? Remember the car is like 5000lbs and if you have the 5.0 if wont be as powerful as you want. Also depends on the incline of the hill, how steep it is.
a. could be the pickup in the tank, even though the guy replaced the pump twice, did he replace the sending unit?
b. still could be vacuum tubing.
c. does it bog down in Overdrive and not in Drive? If it has plenty power in Drive and lacks in Overdrive climbing this hill I would say that is normal because the gear ratios are more advantageous in Drive than OD.
d. another thing is to check the vacuum hose on the EGR AND remove the EGR and clean off the needle with some Carb cleaner. It could be carboned up and sticking.

Lets see what he says?

 

Was told that my direct injection port may be bad!! Does anyone agree??

 

Ok, not that I know alot about cars but here is my two sense. My van bogs down when I press the accelarator down. It has no power going up hills, even small ones. Had it scanned and was told it is the Temp. Coolant Sensor. I am now trying to figure out where that is located on my 1998 Chevy Express 1500 and how to replace it. Maybe this is the issue with your vehicle as well??? Any help?? RacerX???