Low city water pressure can and will effect the opereation of the tankless. I would preform this test with 1) The fresh water pump in operation only. 2) City water only. 3) City water with pump assist. I can align the water for dry camping, connect city water, and turn on the pump if needed.
I have dealt with techs at Gerrard (very helpful) and yes we had to have ours replaced (4hrs to replace by the dealer) and it is a major difference in temp. No adjustment for temp control on the Gen 3 tankless unit itself. The manual shows a white knob (water flow) on the back of the unit and I can see it when replacing the house canister filter, but way to far in there to reach.
** Mixing type facuets must be at full hot water only. Any manual mixing of cold will not allow the tankless heater to operate correctly. If your water is to hot or to cold adjust the temp at the control panel only.
1) The DW has on occasion had the shut off valve on the shower head (inside the RV) in mid position and that caused issues taking a shower.
2) My house canister filter clogged once (reduced flow pressure) and now we use additional filters. Depending on the quality of water I will use dual blue torpedo type filters in addition to changing the house filter often(r).
3) By tech at Gerrard the only adjustment to the Gen 3 is the temp control panel inside bathroom.
All my faucets inside the RV are mixing type (Yuck). The only true testing is at the outside flushing connection. You will need a stopwatch, meat thermometer, and a 5gal bucket.
1) Remove the spray head on the outside flushing station.
2) Cold water only, record the cold water temp (this is your ground water temp)
3) Hot water only, record the max temp (during filling the bucket)
4) hot water only, record the time it takes to fill the 5gal bucket, full stream (hot water)
Simple testing. Remember to preform these test three ways. As stated before ensure the filters are new (or removed for testing purposes). After you have those recordings, call Gerrard and discuss with them on actions.
Good Luck !!