Why do I loose power when in drive and trying to move, but car idles fine and can be revved to the floor?

Started with repairing a burnt plug wire clip. Pulled battery cable to reset computer. Car idles fine, purrs like a kitten, can rev the engine to the floor. No spits no sputters and sounds fine. Put the car in gear and is still OK, accelerate and its power dies to almost nothing like it would in a standard starting in high gear.
Someone I spoke to here said it could be some sort of coil or electrical arching.
Any suggestions as what to look for?
Sorry, can't donate, I'm broke.