Long Term/Short Term Fuel Trim Values

In a continuation of figuring out my hestiation/stumbling problem with my 96 yukon.....

I have just one question this time...

This morning with a cold engine, started it up and took off, at least I attempted to take off. With the gas pedal depressed and the throttle position sensor around 40-50%, the engine would stumble/hesitate with sound of popping(backfireing?) coming from the exahaust lines. I noticed the long term fuel trim would drop to 0% and I think the short term also dropped to 0%. The computer was still in open loop mode.

Should the long and/or short term fuel trim values be something other than 0% during a moderate acceleration?

Thanks,
Omar