No Turbo

If you have 35" of boost, the turbo is running.

To explain it simply, the turbocharger always attempts to operate at full boost as driven by the exhaust, and the Waste gate dumps whatever is excess.

If you are not getting over 35", either the turbo is not getting up to speed or the waste gate is not closing all the way.

The fist thing to do would be to remove the muffler and have a look inside.

The Waste Gate hatch should be relatively clean (For an exhaust!) and close flat against the seat.

The Operating Arm should operate smoothly and not have excessive play in the bushings.

The Turbo Impeller should turn freely, it Will have some play in the bushings.

The waste gate is the common culprit.  It operates in a hot dirty enviroment without lubrication.

If nothing is out of the ordinary you will need to inspect the assembly on the bench.

i think 35" is not up to the required engine RPM @ 5800 and WOT when you take off. see the attached fig. Throttle vs turbo boost pressure from Heavy maint. manual.

Problem looking at waste gate.

If a turbocharger doesn't produce enough boost pressure, it won't work. ... Low pressure can also be caused by leaking lines or gaskets (allowing pressure to escape before driving air into the cylinders, improper filter maintenance, and a worn or sticky poppet valve can also cause this condition.

and

Check the waste gate lever for free movement. If it does not move freely, lubricate the axle of the waste gate with LOCTITE Anti-Seize 8151, ROTAX part no. 297434. Bowden cable, rope sheave and spring for waste gate control.Adjust Bowden cable with M6 hex. nuts (15) so that no clearance is perceptible on waste gate lever. With this adjustment set, pre-tension the pressure spring by 1 to 2 mm (0.04 - 0.08 in.) at straightened cable with the adjustment screw at support.

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you have Waste gate sticky, and look the following remedies:

This is because of  Oil, heat, corrosion etc. causes the waste gate to stick.

Use penetrating oil and make sure the waste gate operates freely every oil change. Adjust the cable properly. The waste gate should be full closed or allowing full turbo at idle and engine off, but it must not be hard at the stop. During initial electrical power up, make sure the cable will pull slightly farther open before the cycle. The cable should be firmly pulling the return spring and should keep the cable taught.

Maintenance: Lube with penetrating oil and cycle by hand until smooth. Operate the servo to check the cable performance.

The engine runs up to 35 inches or maximum continuous 100% OK, but as soon as full turbo (115%) is selected the engine boost pressure also go beyond 35 Inch to 40.5 Inch.

Take off at 35 Inch risky.