HOT water going luke warm is due to cold being mixed with the hot.
Only 2 ways for that to happen
Water heater BYPASS Valve NOT CLOSED (LEAKING THRU)..........otherwise it will flow into HOT line overcoming the check valve in hot out on WH tank
OR
SHOWER (outside one or inside one) only turned off with lever/button on handle vs hot/cold knobs closed.
Cold water will overcome hot inside shower faucet
And NO.....heat source will NOT make a difference.
Your 2007 Vintage uses the SAME set of t-stats for propane and electric....so same temp on either heat source
140*F/T-stat OPENS
180*F/ECO OPENS if t-stat fails (ECO---Energy Cut OFF/High Temp T-stat)