SR22 pilot reported partial power loss during a climb in icing conditions. Pilot diverted to another airport after noticing two cylinder heads were not running normally.

Narrative

Preflight was without issue. Approximately 68 gallons of gas; right greater than left tank; less than 7 quarts oil; at 3.8 and 3.7 gallons. Preflight included prep for icing and wetting out the flight surfaces. Fuel sump was normal. Run-up was equally uneventful. Approximately 30 RPM drop on each left and right mag; no stall at idle. All CHTs were in the green prior to the run-up. Idle was at about 870 RPM or so. Engine ran very smooth on the ground. IFR flight plan to ZZZ; expecting 9;000 ft. Normal takeoff on Runway XX. Given the gusting; ran a bit faster before rotating to accommodate any gusts; so rotated closer to 75+. Plane handled nicely in the initial climb. Flaps up a bit late on purpose. As we approached clouds on the climb; flight into known icing re-enabled. Climbed well per ATC instructions up to 9;000 ft. At 9;000 ft.; I was still in the clouds east of ZZZ1; so asked ATC for higher to avoid using all the TKS solution. They gave me climb to 10;000 ft. Attempted to climb and the plane would not climb. Felt a rumble in the plane. At first; thought it might be the front wheel in the wind; but that did not explain the failure to climb. Thought it might be ice; but was running and no sign of ice on either wing or windshield. Then I noticed the engine display and had lost CHT on #5; and as I recall #2 was also very minimal - small white bar. In trying to recall; might not have been #2; but two cylinders were not running normal. I think all of the cylinders were lower than they should have been. Boost pump on; mixture full rich. Throttle was already wide open as at that altitude; WOT (Wide Open Throttle) is less than 75% power for a 22. Plane still would not climb and was rattling.Asked ATC to return to ZZZ1 and immediately lower. They gave me 6;000 ft and later; a direct ZZZ1. Performed an emergency descent with right turn to get to lower altitude of 6;000 ft. KIAS approximately 180 - 90 or so. Engine started running better; CHTs came up. Flight into known icing back on because I'm now back in the clouds. Handed to frequency. I wasn't going to [request priority handling] as the engine was now running better… but ATC wanted the [the priority handling requested]. Direct ZZZ1; visual to [Runway] XX. No further issues with the plane on the return. Was a bumpy return; moderate turbulence down to the field; wind shear +/- 10 kt. Landed successfully and exited on [Taxiway] 1. Taxi to FBO.