SD Altitude tuning P01 GM HPtuners

411 P01 PCM running HP Tuners 3 Bar OLSD OS: 1263016.

C5 Corvette. Procharged LS6, 5.7l , 850rwhp or so. Dart heads, donkey cam 238/254 16 deg overlap. Low vac at idle (72 Kpa at 100kpa baro). Smoke tested no vacuum leaks. ZR1 LSA 3 bar map sensor.

Tuned VE to under 3% error at 700'. Runs excellent all around at that altitude. Beat the snot out of it on the "Tail of the Dragon" without issue.

Problem this weekend: Tuned at 700' and drove to 6000'. With the altitude change, Fuel was showing 15-25% lean everywhere part throttle/out of boost. I'm seeing Kpa levels at altitude with some throttle that I'd only ever see at no throttle decel at sea level. But basically everything under boost was lean, so I didn't run it to hard to see how far it would be off under boost.

I believe the issue is that there is way more load on the engine at the same MAP levels when I am at elevation than sea level. The large cam isn't really working with me here.

Is there a way to add correction for barometric changes? I have the VE correction factor tables as stock, but believe that strategy is disabled without the MAF functioning. Any strategy to pull baro from the map sensor would just max out to 105kpa whenever I get into boost.

I did have an idea to make a (relatively simple) electrical box with an ambient baro sensor and use that output to modify the MAP signal before it gets to the ECU... but that's almost trying too hard to make the stock ECU work.

Am I beyond the bounds of what the factory ECU can handle? I know eventually I'll go aftermarket (leaning haltech) to take advantage of other features like wideband Closed loop control and traction control. Timing control by gear would be great to make 1st and 2nd gear a bit easier to control.

Reading Haltech corrections descriptions sounds like a strategy that may work for what I need:

MAP Correction

The percentage correction table for changes in Manifold Pressure. Up to 3D mapping is available with this table. When the Tuning Method is set to VE and when the load source is TPS, the Manifold Pressure is automatically corrected for, as part of the VE fuel calculation. In this case, the table should initially be set with all values at 0% (default). The table is then used as a correction for any error in the automatic calculation.