Originally Posted by red_2005_convertible

Hi SRT6exy,
Sorry, I should've check the manual first instead of googling what the dtc were. I checked the service manual on DTCs P0715 and P0720. Have you downloaded the service manual from this site? It's very helpful. Here's what the manual says P0715 and P0720 (see:below). One thing to note is that for either one, it's recommended to check the transmission fluid level.

(P0715) N3 INPUT SPEED SENSOR CIRCUIT (CONTINUED) page 21-106
When Monitored and Set Condition
² When Monitored: Engine speed greater than 450 RPM, no engine speed DTCs, no TCM undervoltage system
operation, no output speed sensor DTCs (signal from the ABS system), all wheel speeds above 250 RPM
(signal from the ABS system), no rear wheel speed DTCs (signal from the ABS system), and no wheel slip
detected (signal from the ABS system), no shifting operation, detected gear is 3rd or 4th and the detected gear
is the actual vehicle gear.
² Set Condition: If the N3 input speed sensor signal is equal to 0 RPM, short signal circuit to ground, shorted to
battery, an open input speed sensor, a faulty input speed sensor, or an open sensor supply circuit.
POSSIBLE CAUSES:
SENSOR SUPPLY VOLTAGE CIRCUIT OPEN
N3 INPUT SPEED SENSOR SIGNAL CIRCUIT OPEN
N3 INPUT SPEED SENSOR SIGNAL CIRCUIT SHORT TO GROUND
N3 SPEED SENSOR SIGNAL CIRCUIT SHORT TO ANOTHER CIRCUIT
SENSOR GROUND CIRCUIT OPEN
SENSOR GROUND CIRCUIT SHORT TO GROUND
SENSOR GROUND CIRCUIT SHORT TO ANOTHER CIRCUIT
N3 INPUT SPEED SENSOR
TRANSMISSION CONTROL MODULE
Diagnostic Test
1. PRE-DIAGNOSTIC CHECK OUT
Note: Low fluid level can be the cause of many transmission
problems. If the fluid level is low, locate and repair the leak then
check and adjust the fluid level in accordance with the Service
Information.
Note: Always perform diagnostics with a fully charged battery to
avoid false symptoms.
With the DRB IIIT, read Engine DTCs. Check and repair all engine
DTCs prior to performing transmission symptom diagnostics.
With the DRB IIIT, read and record all Transmission DTCs.
Note: Check connectors - Clean/repair as necessary. Poor pin to
terminal connections can set DTCs.
Using the wiring diagram/schematic as a guide, inspect the wiring and
connectors. Repair as necessary.
Most DTCs set on start up but some must be set by driving the vehicle such that all diagnostic monitors have run.
Note: Check for any Technical Service Bulletins that may apply.
Perform this procedure prior to Symptom diagnosis.
Continue
Go To 2


(P0720) CAN BUS CIRCUIT (CONTINUED)
When Monitored and Set Condition
² When Monitored: Always monitored with system active at each ignition cycle.
² Set Condition: Open circuit in the CAN C BUS (+) circuit or CAN C BUS (-) circuit, short to ground of CAN C
BUS (+) circuit or CAN C BUS (-) circuit, short to voltage of CAN C BUS (+) circuit or CAN C BUS (-) circuit,
CAN C BUS (+) circuit shorted to CAN C BUS (-) circuit, or a TCM failure. Note: All CAN message missing
DTCs will also be present, which indicates a complete BUS failure.
POSSIBLE CAUSES
CAN C BUS(+) SHORT TO CAN C BUS (-)
CAN C BUS (+) AND/OR CAN C BUS (-) CIRCUIT OPEN
CAN C BUS (+) AND/OR CAN C BUS (-) CIRCUIT SHORT TO GROUND
CAN C BUS (+) AND/OR CAN C BUS (-) CIRCUIT SHORT TO ANOTHER CIRCUIT
CONTROLLER ANTILOCK BRAKE (need to check this connection)
POWERTRAIN CONTROL MODULE (you already checked this connection)
TRANSMISSION CONTROL MODULE (you already checked this connection)
Diagnostic Test
1. PRE-DIAGNOSTIC CHECK OUT
Note: Low fluid level can be the cause of many transmission
problems. If the fluid level is low, locate and repair the leak then
check and adjust the fluid level in accordance with the Service
Information.
Note: Always perform diagnostics with a fully charged battery to
avoid false symptoms.
With the DRB IIIT, read Engine DTCs. Check and repair all engine
DTCs prior to performing transmission symptom diagnostics.
With the DRB IIIT, read and record all Transmission DTCs.
Note: Check connectors - Clean/repair as necessary. Poor pin to
terminal connections can set DTCs.
Using the wiring diagram/schematic as a guide, inspect the wiring and
connectors. Repair as necessary.
Most DTCs set on start up but some must be set by driving the vehicle such that all diagnostic monitors have run.
Note: Check for any Technical Service Bulletins that may apply.
Perform this procedure prior to Symptom diagnosis.
Continue
Go To 2