The post indicates you want it free or cheap. Is your truck the Vortec 7.4-liter V8, or a 5.7-liter V8, or a Detroit Diesel 6.5 L V8 and what year? This is about getting 10 new ones. Is it a pressurized cap which should minimize the search a bit. Is it rated a 16psi cap?
If the truck is NSN 2320-01-123-2665 then the General Motors fuel filler neck is P/N 14063325 which is NSN 2590-01-155-7965 so now where did that "special cap go?
View attachment 716351
The Cap, filler opening is P/N 14063326 which is
NSN 2590-01-155-5063
To buy seems to be unobtainium, so why am I thinking 1 ton diesel chevy pickup here. Trying to find dimensions tto cross reference.
https://www.youtube.com/watch?v=taDKWkphZjs
It is a GM part 14063326.
View attachment 716354
Stant 78225
Overall Height: 2.725 inches nominal
Style Designator: Threaded type (external)
Outside Diameter: 2.830 inches nominal
Stant says they are available
Part Number 30600-A1 Specification
Part No. : 30600-A1 Manufacturer : Stant Mfg Co Inc Cage : 78225
NSN : 2590-01-155-5063 Description : Cap,Filler Opening
FSC : 2590 Miscellaneous Vehicular Components
In this PDF is 1095 diesel fuel filler caps made by Stant to look thru for the match.
View attachment 716354
View attachment 716351 for 50 bucks