I'd bump your timing up more to 38 degrees and lock it out first.
Fixing the WOT issue will help it get going down the track better but will do nothing for your stumble.
To me it sounds like the accellerator pump circuit(s) need attention.
Make sure you dont have any slack in the arm(s) that operates the pumps, adjust the screw (longer) till you have zero slack and your getting a full shot as soon as you move the throttle blades.
I'd also reccomend a 50cc pump kit in the front of any all out racemotor, especially footbraking it.
There's more to tuning a accel pump circuit than meets the eye, different cams profiles, many different squirters sizes, etc it can get pretty involved in a hurry if this is uncharted territory with you then you might do well to get someone in the know to look at it with you.
Now you say it's hard to get cranked and keep running, especially in drive?
Is it loading up? idling to rich? Black smoke? Your eyes tearing up?
If it is then you'll get a bad bog simply because your plugs are all loaded up with fuel, You need to correct that as well either by setting the float levels correctly or by adjusting the idle mixture screws in or you could have blown power valve. Check for fuel drippiling out of the boosters at an idle.
This is going to be a process of elimination, only do one thing at a time if possible even though it may be a multitude of things causing your problem.
Next time you go to the track be prepared to make adjustments between rounds, leave what helps and put back what doesn't.
Goodluck, Cp