If you have a Ford truck you are prolly miss'n one or more of these silly caps. I run a 2005 F250 Superduty but these should fit F150 as well as other Ford models around that time frame. I designed them so they actually latch in; instead of gingerly sitting on the lip surround and just waiting for that next pot-hole impact to fly out.
You can grab my 3D model here: http://www.123dapp.com/stl-3D-Model/Ford-Grab-Handle-Caps/618451
and use the free 123D app by Autodesk here: http://www.123dapp.com/123d
to mod if you like (add your initials to the tops of the caps) and then export to your preferred format for 3D printing; here is a sample workflow I have used at home designing and printing with great results: http://www.instructables.com/id/Basic-workflow-for-3D-design-in-Sketchup-and-3D-pr/
These caps take me less than 30min a pair to print and have been tested vigorously on fairly horrible roadway/fields. I only had black ABS filament but you can source grey or beige plastic too if your after that near OEM look.