I have been flying an A36TC (EA-113) for about 30 years. I have found the best climb power setting is generally to us 36 in. Hg and 2700 RPM for take off and initial climb to a safe altitude (i.e. whatever you are comfortable with between 400 and 1,000 feet AGL), and then I set the cruise climb setting 34 in. Hg and 2600 RPM. It is always important to not climb at a lower power setting than 34/2600 as the automatic controller will reduce fuel flows, which could result in overheating the engine, as it relies on high fuel flows for cooling in climb since there are no cowl flaps. I always transition to the cruise climb airspeed of 120 kts. once I make the power reduction to 34/2600,unless I have a specific reason to use Vy or Vx to facilitate engine cooling. On a hot day, I may even use a higher climb airspeed like 130 kts. to facilitate engine cooling.
The engine should be able to hold manifold pressure to its critical altitude of 19,000 feet bearing in mind that depending on atmospheric conditions and how your controller is adjusted that may be 34 to 36 in. Hg. If the engine will not do that you definitely have a maintenance issue; it could be any one of a number of things that have been mentioned (i.e. intake leak, exhaust leak, obstruction, a turbo problem), and I reccomend you get it fixed, as there are very few problems with the turbo-charged engines that I have found to be benign.
As a starting point, I would suspect that your problem is either an exhaust leak or something in the turbo unit as the fact the fuel flow is going down commensurately with the manifold pressure shows the controller is reacting to lower manifold pressure and reducing the fuel flow just as if you had intentionally reduced power, but that is just a guess.
Finally with regard to using Low or High Fuel boost in climb, it is important to know whether or not your airplane has a kit installed that was the subject of a Beech Service Bulletin about 25 years ago. The A36TC initially had smaller diameter fuel lines and it was a common operating procedure to go from low to high boost in take off and climb at higher density altitudes. The fuel pump switch had three positions (Off-Low-High/Low), and in the High/Low the pump would automatically switch from Low to High at approx. 25-30 in. Hg However some pilots failed to realize that when going from low to high boost one needed to immediately lean the mixture; otherwise the engine could flood and fail. Beech addressed this with the SB and Kit.
Airplanes with the kit have larger fuel lines and the fuel pump switch has the following positions: Off-Low-High. It is not recommended under any circumstances to use the High setting in flight unless the mechanical fuel pump fails. The only other use of the High setting is to prime the engine as part of starting it.
Hopefully this helps.