Lovin the K-2500 but!

[rocketmanpete]

My 00 K-2500 has been great however here is the problem. She starts up and runs fine on CNG maybe 5 to 10 miles then she switches to Gasoline. Shut her down she starts fine again on CNG then back to gasoline it tripped the check engine light also. So my guess from reading it may be the hpr filter. Also where can I get a parts list/function and location schematic any and all help greatly accepted If the info is here on site please point me in the right direction. I have very limited free time at home.