You should not be changing blower speeds without also check air flow ( CFM). One explanation for the rise is that with a higher blower speed, moving more air, the in/out ērise may be lower, but the house would heat up faster as more "heat energy" is being produced.
Here is a brief section from your install manual:
Temperature rise must be within the range specified on the unit
rating plate. An incorrect temperature rise may result in condensing
in or overheating of the heat exchanger. An airflow and temperature
rise table is provided in the Specification Sheet applicable
to your model*.
CIRCULATOR BLOWER SPEEDS
TO AVOID PERSONAL INJURY OR DEATH DUE TO
ELECTRICAL SHOCK, TURN OFF POWER TO THE
FURNACE BEFORE CHANGING SPEED TAPS.
This furnace is equipped with a multi-speed circulator blower. This
blower provides ease in adjusting blower speeds. The Specification
Sheet applicable to your model* provides an airflow table,
showing the relationship between airflow (CFM) and external static
pressure (E.S.P.), for the proper selection of heating and cooling
speeds. The heating blower speed is shipped set at “B”, and the
cooling blower speed is set at “D”. These blower speeds should
be adjusted by the installer to match the installation requirements
so as to provide the correct heating temperature rise and correct
Use the CFM LED (green), adjacent to the integrated control
module fuse to obtain an approximate airflow quantity. The green
CFM LED blinks once for each 100 CFM of airflow.
1. Determine the tonnage of the cooling system installed with
the furnace. If the cooling capacity is in BTU/hr divide it by
12,000 to convert capacity to TONs.
Example: Cooling Capacity of 30,000 BTU/hr.
30,000/12,000 = 2.5 Tons
2. Determine the proper air flow for the cooling system. Most
cooling systems are designed to work with air flows between
350 and 450 CFM per ton. Most manufacturers recommend
an air flow of about 400 CFM per ton.
Example: 2.5 tons X 400 CFM per ton = 1000 CFM
The cooling system manufacturer’s instructions must be checked
for required air flow. Any electronic air cleaners or other devices
may require specific air flows, consult installation instructions of
those devices for requirements.
3. Knowing the furnace model, locate the high stage cooling
air flow charts in the Specification Sheet applicable to your
model*. Look up the cooling air flow determined in step 2
and find the required cooling speed and adjustment setting.
Example: A *MV90704BXA furnace installed with a 2.5
ton air conditioning system. The air flow
needed is 1000 CFM. Looking at the cooling
speed chart for *MV90704BXA, find the air flow
closest to 1000 CFM. A cooling airflow of 990
CFM can be attained by setting the cooling
speed to “C” and the adjustment to “-” (minus).
NOTE: Continuous Fan Speed will be 56% of
high stage cooling.
4. Locate the blower speed selection DIP switches on the
integrated control module. Select the desired “cooling”
speed tap by positioning switches 1 and 2 appropriately.
Select the desired “adjust” tap by positioning switches 3
and 4 appropriately. Refer to the following figure for switch