Your 2015 Vista's V-10 pulsing issue that started after mountain passes in Montana is likely caused by a failing mass airflow sensor, throttle position sensor, or fuel delivery problem. The "Fault received from External Node" code suggests a communication issue between engine management and instrument cluster that may be related.
Girard GG1000 motion sensor can usually be disabled by pressing and holding the extend button for 5+ seconds after fully extending. This allows use of support poles and sun shades. Re-enable by holding retract button when done.
Kwikee steps stuck retracted with amber light usually indicates motor failure or linkage bind. Check 12V at motor first. If power present but no movement, replace motor. Lubricate linkage as preventive maintenance.
A slow-draining gray tank is typically caused by grease buildup, soap residue, or debris in the tank or drain pipe. Most issues can be resolved with tank flushing, valve cleaning, or using specialized RV tank treatments.