leehatten,
One things for sure, with todays craptastic gas, our cars can't handle 19 psi without aluminum heads and or a front mount intercooler. If your chip has 19-20* timing under WOT, you could see detonation at 19 psi especially on a street chip. And of course, the colder temps will raise your boost level. If it was at 15 psi during the summer, it could very possibly go up to 19psi in colder weather, especially if you're utilizing the stock 21 year old wastegate solenoid and wastegate actuator. 15-16 psi has pretty much been the safe level for years.
Your stalling out and or fluttering issue when below 1/4 tank could very possibly be an innacurate fuel level gauge. It's very common that the gauges can be very innacurate on the factory gauges, I've had one be off by as much as 1/4 tank. If I tried to run that car down to 1/4 tank, it would stall, spit sputter and even die on me. It happens with age.
Now days, unless the car has a new sending unit and an extra ground strap from tank to frame, I try to fill up when the needle gets between 1/2 and 1/4 tank.
The only real way to know for sure if your gauge is off, would be to drain your tank completely dry, and fill it up with a preset amount. Then noting where your needle is for that preset amount. Very time consuming if you ask me. The other method would be to install a temporary fuel pressure gauge that you can see while driving. Let the tank get down to 1/4 tank. Make a run and watch the fuel pressure gauge. If your fuel pressure starts wildly fluctuating or you get the dreaded bouncing needle, this is a sign that your pump is sucking air from either fuel slosh or low fuel level.
I never recommend racing/WOT runs on a 1/4 tank of gas with factory sending unit/tank. It's a recipe for destruction.
Hope this helps a little.
Patrick
Scan master read about 12 * knock. 
I will look at replacing the wastgate line and the waste gate. Should I go ahead and get the waste gate solenoid as well?
