1995 Trooper

Having problems maybe one of you guys can help. Have an Isuzu Trooper that has sat for 3 years. Decided to get it going again and have. I flushed old gas out, changed all belts and all fluids. It drove fine in the snow for the first time all day. A dying problem developed more and more throughout the day, until it got to the point that I could only go 20-30 feet at a time and had to put in nuetral and restart. Idles fine but anytime I put a load on it such as putting it in gear or 4x4 it dies. I was told to replace the fuel filter. I just did that and let it idle for 15-20 minutes. It works a little better in 2 wheel drive but still dies every 50-60 feet. Alternater I just checked and it is good. New battery. Any suggestions?