Hi, I recently purchased an Audi A4 3.0 V6 2002 B6 and ever since I've had it it's had a horrible misfire. This misfire occurs when you plant your foot, the car does not pickup very fast and feels sluggish. Also the vehicle struggles a lot to go up hills.

I connected my scanner to the vehicle to find the problem with the misfire and the codes I got were:
P0300,P0301,P0302,P0303(random multiple misfire)
these are all misfires on Bank 1 which are cylinders 1, 2 and 3 (UK drivers side bank) I decided to just change the spark plugs as I thought it's either the plugs or coil packs so I replaced all 6 of the plugs and also switched the coil packs from cylinders 1, 2 and 3 with 4, 5 and 6 (from bank 1 to bank 2) I thought this should fix it and if the coil packs were bad the misfire should continue on to the opposite bank as I switched the packs around. Unfortunately, the misfire was still in bank 1. I checked all the cylinders on my scanners live data and 1, 2 and 3 would still miss and occasionally 4, 5 and 6 but it's rare (I think it's because of the imbalance) I do not suspect a bad headgasket or worn piston rings as there is no blue smoke and the engine oil is on point and likewise with the coolant, it's all there and the car does not smoke. Since then I have done the following:

New fuel filter
New spark plugs (as mentioned)
Switched coil packs (as mentioned)
Checked for vacuum leaks throughly
New intake manifold gaskets
Checked the wiring
Cleaned battery terminals (battery is weak however)
All fuses replaced

From doing all of this the car still misfires, on idle it's fine and there's no misfire only when you drive. Recently also, when I connect my scanner up to the car the vehicle does not communicate with the scanner at all I've checked the fuses and the EML comes on it only connects to the car when the ignition is off which is really odd. However, this is no good as I cannot view live data and the scanner capabilities are limited. I am really stuck and do not know what else to do the car is driving me insane! Any help would be greatly appreciated!!