8.5MS3 makes valid observations. Maximum torque is at about 3200 rpm. Maximum torque when the engine is under maximum load is a potential problem on this engine. 5th gear is good for 107 shifting at 5,500 rpm, and about 117 if you want to go to 6,000 (which is where thermal ineffeciency of the turbo becomes pronounced.
So unless you really want to go faster than 107-117, it's much healthier for the engine to drop down to 5th and out of overdrive when accelerating at that speed.
But I am puzzled by the OP's report. Perhaps he could better explain to us what he is experiencing - light throttle, full throttle, what else may be happening. If the boost is rising and falling, this would not be a bpv leak, as it would simply not be able to hold the boost, and he should be having a similar phenomenon in 3rd, 4th and 5th at the same engine rpm and throttle position.
Without more info, I'm a bit baffled. He might want to see if someone could temporarily hook up a boost gauge to see if boost is falling and rising in some strange manner under those driving conditons or whether this might be something else. Better yet would be access to some type of data logging such as Dash Hawk, if he could borrow one. There could be fuel pressure problems, there could be subtle ignition problems, it's really hard to tell. If it is boost leak, it could be anywhere in the pressurized side of the system from the turbo outlet, intercooler core, intercooler outlet and to the intake manifold and all the hoses and couplings in between, not just the bpv. Apparantly there are no check engine lights on. I just need more info.
