I don't have a lot of technical info, so I am sure others will help you out regarding the possible fuel issue.
If your NSBU switch is the problem....I can tell you when my NSBU went south it caused the gear indicator to flash. I bought mine from an Allison dealer for about $50 (IIRC). Aside from having a difficult time getting one electrical connection to come apart, replacement was no big deal laying on the garage floor. I bet it didn't take over 45 minutes, going slow and following the directions from this web site. If you do a search you can probably still find them. So $500, way out of line.
Dawg
2002 D/A, Crew Cab S/B 4x4, Light Pewter Metalic, Built 10/12/01, Arrived 11/07/01, LineX, Husky Flaps, Husky floor liners, Lund hood protector, A.R.E. 'Z' Series cap, AutoMeter Boost and EGT gauges, Prodigy brake controller, Cougar 294rls. Member #5013