2002 sonoma dies in reverse

I just got a great deal on a 2002 Sonoma from my brotherfor $1000. It has been running fine until the other day when it died in reverse. It seemed a little slow to crank but started, then as soon as I was in reverse it died. This happened a couple of times. It starts but I have to keep my foot on the gas pedal to keep it running and sometimes that won't even work. After it dies the battery light stays lit but there is still volts in the battery. I am confused at where to start looking for the problem. Help?

What engine is in the vehicle? Is the SES light on? When was it last tuned up? What parts were replaced? What brand of parts were used? Does it crank slowly or does it take excessive cranking to get it started?