Vibration after a re-gear is probably driveline related. It was there after you added the lift, but the increased driveline speed aggravated it. This simply could be cured with some wedges that correct pinion angle. The angle of the driveling coming out of the transmission needs to be the same as is is going into the rear differential so the u-joint's can work in unison.
Anther thing to note is the front driveline, from the factory the yokes come out of phase. This means they are 90* off from each other - not a problem until you add a lift and change the driveline angles. This vibration will only present itself in 4X4.
For the lack of power I would start with the basics. Check and make sure the MAF sensor is clean, fuel filter is not plugged and air filter condition.
Any codes present?
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