Naf

iTrader: (1)

You know since the car is runnin fine again, i would visit your tune guy.

Probably what happened was after sitting so long it lost its LTFT so it had to relearn thus the loss of power. If you have EFILive of HPtuner, just log the STFT and LTFT and then add that as a % to the MAF, that will help you below 4000rpm. you need a dyno for above 4000rpm...

vmapper

iTrader: (8)

Yes, Depending on what exactly the OP meant. One possible reason is a common '**** tune' or the typical shitty calibrator - there are more of them than good ones. Especially idle temp variable tables (e.g. RAF).
Dyno can be and should be used for ALL rpm. (steady state tuning) to really dial a vehicle in. (Both MAF and VE if running blend)

Naf

iTrader: (1)

Not really the dyno cannot take into effect aerodynamic drag.

I normally tune the top end on the dyno, then tweak the bottom end on the road. The Long Term Fuel Trim, LTFT, and Short Term Fuel Trim, STFT, really help in adjusting the VE/MAF for changes in the engine.

vmapper

iTrader: (8)

Dont want to get into too much into this, but drag is irrelevant as what you are NOT able to on the street is handle transients. Changes. which is exactly what one does not want. On a Steady State dyno, you can vary engine loads (throttle) without any changes in speed and have good solid measurements for each cell exactly, you are not even remotely close to being able to do this on the street. You are not going to be able to target a kpA row and go through each RPM column on that row with good count numbers, it is impossible. However, you can precisely determine cell values due to exactly that...removing drag and road slope changes and you lightly letting off and on the throttle. - any transient fills. You are never going to get a tune on the street dialed in as good as you would on a steady state dyno. Talk to Greg Banish for details and better explanations.
Also something to note: you having LTFT on means you are overwriting your top end tune over time. Values are added when LTFTs reach a certain constant count. Id turn LTFTs off if I wanted to keep my top end calibration how I intended it and only run on STFTs. Ive done street tunes and Steady State tuning is easily noticeable with throttle responses, especially where it counts... drivability rpm range. Hope that makes sense.