1995 Chevy Silverado Engine Surges, No Power, Doesn't idle

I have a 1995 Chevy Z71 5.7L with 250,000 miles on it.

Truck doesn't idle well, no power, surges, and it's running extremely rich. The service engine soon light comes on after running a while. I believe the codes were "34" and "44" when we checked. One of those was the O2 sensor and the other was something on the throttle body (can't remember!)

I replaced O2 sensor, but not the throttle body because I saw that the timing chain was messed up I wanted to replace that first because I wasn't sure if that was causing the problems or even if that was causing any codes to come up. After the chain was installed, still ran bad. Checked the timing, the mark on the balancer was off the plate ( maybe an inch or so before the plate so that the mark on the balancer was pointing straight up ).

Do I need to adjust the timing? And if so, where is the wire to bypass the computer?

also, how I do check for other potential cause for this problem?

Thank you! :)