Thanks for all the suggestions so far. I have a 91 b2200 with the extended cab. Anyway I was having trouble with my truck, I took it to a mechanic and I got tired of his BS and just decieded to fix it myself. The truck would sometimmes slow down going up steep hills and I could barely keep it going. Other times I could pull out on the interstate and it would do the same,slow way down. Well I have the webber carb put on and one thing I found was what I think is the fuel pump was mounted to the side of the engine to the back. IT had 2 hoses going in and one out and that one went to the carb. One of the hoses going in had a crack and was allowing it to air in . I think this may have been a line to allow the vapors to go back maybe? Anyway I replaced that one and the others are good and tight. Now it drives perfect except when I get to about 1/2 a tank it sometimes will do the sluggish bit again. So yesterday I checked towards the back at the tank. What I found out is that the main hose from the filler tube to the tank had the clamp broke and was loose. I also found what I think is the vapor tube and it had a crack at the top also. So I moved that up and clamped it so it would not loose pressure. My question is if the tanks filler hose is loose and does not keep pressure can this to cause it to be sluggish when it get to 1/2 a tank or less?

 

I'm not totally sure but I do know if the system isn't holding a certain pressure it will NOT run right. So this is a possibility.

 

I would just make sure that you have a good gas cap seal. You might also want to check the hose lines that run down to the actual tank. sometimes the rings that hold them in place are worn and break.