'95 GMC 5.7L Wont stay running.... HELP

[modman7x]

The truck has 267,000 miles, but a new engine was put in 24,xxx miles ago. It is not a used one, but a new gm engine. The problem I'm having is this. The truck will start and idle fine, but when I go to drive it, it spits and sputters, and sometimes will even die. Seems like the longer I drive it, the worse it gets. I have changed the cap and rotor, pulled and cleaned the I.A.C. motor, replaced the fuel filter. It died on me the other day, and the check engine light came on. When I pulled the codes, it said "o2 sensor", and "Low Idle". I did find a vacume hose off of the throttle body, but when I plugged it in, it didnt change anything.

Any help would be great.

Thank you