86GT50

Ok, here is my problem
I have a Stroked 347 in my 86 Mustang and when I go to jump on the car, it doesnt want to go anywhere..... it starts to break up REALLY bad, but when I have the car out of gear or if the clutch is pressed in, it free revs great & without problem??? I have the timing advanced to 10, the car starts up fine, idles ok, it doesnt break up at all when I free rev the car to a high rpm when out of gear, but when I put it in gear & take it for a test drive, it breaks up crazy when I get thr rps's up & over 2500.....
I have the MSD Digital 6, I've changed the coil to a brand new PS91, put in brand new NGK plugs gapped to 45, brand new ACCEL hi-temp wires...... I cant figure this one out. this started to happen before I changed a few things on the car so I didnt think much of it because I was about to change up my combo & when I pulled the old wires off the car, a couple of them were burnt from the headers & cracked in various places so I assumed that was the problem.......
What I had on the car was the Edelbrock Performer RPM-EFI, 24lb injectors with MAF calibrated for them, stock fuel pump, stock coil & the EGR hooked up. The changed i've made are the following: MAF & 36lb injectors, 255 fuel pump, Edelbrock Victor EFI, MSD 8456 Distributor, Accell hi-temp plug wires, New NGK plugs, EGR Deltete, Removed the PCV & put in a breather into the valve cover. So thats it, this is where i'm at, the car sounds & responds great, in neutral, but in gear..... NOTHING / BREAKS UP....... any help here??????? Can the Digital 6 be bad??? is my timing off??? Do I have the wrong gap on the plugs????? also, what plugs do you reccomend???
I put the car up on jacks last night put back on the mufflers & tested the car & it didn't give me a problem when I went through all the gears. I am changing the cap & rotor on the distributor to see if thats the prob, but upon initial inspection, there seems to not be any cracks in it... but who knows at this point...... PLEASE HELP WITH ANY POSSIBLE SOLUTIONS THAT I HAVE NOT THOUGHT OF OR TRIED ALREADY