Have your dad check the codes by turning the key (on is not start, just the position right before it) on-off-on-off-on and counting the flashes the power loss light makes. It will flash one group, then another shortly after. So if it flashes twice then flashes 5 times you would have a code 25, three flashes then six, would be a code 36, etc.

 

Is there still the little bleed/restrictor orifice in the WGA to WGA solenoid line? If not the wastegate is possibly being held open.

 

If the head was off recheck the vacuum harness behind the valve cover especially if the plastic harness is still intact,the plastic lines break and you wil lnot see them.If any of those lines were repaired with a vacuum tubing splice be sure all the lines are connected to the right spot.

 

Check your cam timing... could be retarded a tooth. Check/re-set your ignition timing as well for that matter. Also, did you use a swirl head (86+) when you replaced it? If you used a pre-86 head, you lost some static compression, which could cause it to feel sluggish. Check the codes though for sure, they could point you right to the problem.