GU patrol power mood swings

[Hodge]

What would cause the power to fluctuate everynow and then ??
For a while now I've been noticing my patrol's very moody when it comes to power. Sometime's it's like me on monday mornings, other times it loves to get up and dance.
I've been trying to pin point factor's which may cause it. Weather, fuel, if the car's warmed up yet or not, etc... But it's a mixed bag of results, nothing really lines up with sluggish behaviour.

This morning for example, drove it for 45 minutes and it had plenty to give. On the way back, it's as if it's running on 2 cylinders, feels very sluggish. Then, half an hour later drove it again, and it's back to it's normal self. It's just very odd and annoying. I'm not talking great amounts of power missing, but it is definitely there for me to notice the difference.
After I got the exhaust fitted, I didn't get it tuned or anything, but my mechanic recommended I get it done to get everything else up to speed with the larger exhaust, and he reckons mine is definitely overboosting. My gauges aren't fitted yet so I can't monitor anything so I don't know whats happening.
I'm just brainstorming but could it be the MAF sending weird messages to the ECU ? I've got the spray cleaner (CRC), just didn't get around using it yet.