On a 94-97 with a stock valvetrain, I'd be hesitant to push past 3500. The reason is that while the stock springs are capable of handling 4000 RPM, at this point they are probably quite worn out and 3750+ RPM at 30+ PSI may present a sealing problem.
At 1.68" diameter, the face of the valve has a surface area of 2.638 sq. in. which means that at 30 PSI boost there is about 79 Lbs. of pressure pushing against the valve. Brand new, the valve spring seat pressure is 71-79 PSI (spec.) and I'm sure they are much lower than that after 100K+ miles. As you can see, it is REALLY easy to push the valve open if you're not careful.
The power will fall off at 1 of 2 points... (1) Wherever you stop injecting fuel or (2) wherever you are not able to get more air into the engine. Generally the fuel control tables on an early motor starts pulling fuel out at 3300 RPM or so. Later trucks are about 3500 RPM.
Hope this helps.
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