intermittent "air print" desperate for help... MB REP 2

[Archangel]

Hello! thank you for taking the time to read!!!
I am just getting started in 3dprinting and have learned a lot in getting started, but now at my wits end.

Here is whats happening:
I start prints just fine perfect smooth stream and i "load filament" to get PLA to the nozzle before each build and to check for clogs.
It build the raft flawlessly and the detach layer works great. but randomly anytime after it starts building the real print it appears to stop extruding intermittently.It creates a small gap between the print-head and the build; which then proceeds to extrude small amounts of filament which forms webs and balls of string. it also appears to not extrude properly just before it starts stringing.
When i try "load filament" to check for extrusion it is slow then suddenly takes off and extrudes perfectly after about 2 seconds.

Here is what i have done so far to try to correct the issue:
I thought it might be temperature so i did research and tried several different temperatures which appears to have no effect.
I bought new nozzles and swapped out the original for an identical.
I completely disassembled cleaned and checked the entire print-head/extruder assy.
I tried different combinations of speeds and build quality.
the drive gear was slipping and if i press the filament in a little but it starts extruding. that seemed to go away after i cleaned the gear.
I would be totally grateful for any information you could provide that might send me down the right path.

PS: Really small things print perfectly but randomly anywhere after a half hour two ten hours later it will start the issue... really annoying!


Thank you AGAIN!!!