You covered all the possibilities.
- clean and lubed gun
- clean and lubed maxflow
- fresh paint (I hope)
- paint to barrel match
- full tank
- pressure between regs
I would check the Bulldog's recharge rate. One of it's reg seals could be dirty and is preventing it from staying consistent. You'll need a reg tester to find this out OR
just put it on your spyder and chrono. If the readings are also inconsistent then it probably is the tank. I have a teammate who used to have this tank and had a similar problem. No matter what he set the output pressure on the tank to, it still fluctuated to at least 900psi. He sent it back to ACI to get it fixed.