There are 2 reasons for that.............
1 - Once max readings start to fall your just revving until the valves float
2 - My tire info was input into the computer before any sessions began, which are Q rated(max 100 mph)
Your valves aren't floating at 3600.
Look to my first post here........3200rpm and you're done.
Since you are making torque to 3600 and since you made nearly 400lbs of torque.......you've done well.
These engines are done near 3500rpm, your engine fell flat on it's face which is exactly what I would expect. To answer the other guys question, there is no reason to run up to 5000rpm, there is nothing there, notta.
Dyno numbers will allow you to tune, let you know where your engine is making power, give you bragging rights.......but.......in the real world, numbers don't mean much. Trans, gearing, tire size, traction.......all that....in the real world, on the street.
Air flow, air flow, air flow.......these engines do not flow. Intake and exhaust limit you for one......cam choice would be another.......I don't recall you mentioning any of that, intakes suck for sure. If anything the intake is smothering any chance of making power above 3500rpm.
Guys expect something that is not there, will never be there.
If you are making close to 400lbs torque..........you got a good puller, you did well.