Below are the AMSOIL oil and filter recommendations for your 2008 Ford F150 4.2L 6 cylinder engine:
2008 FORD TRUCKS F150 PICKUP 4.2L 6-cyl Engine Code 
The 4.2L V6 with iron block and aluminum heads puts out 202 horsepower with 260 foot-pounds of torque. This engine is a great candidate for AMSOIL synthetic motor oil and hopefully you are looking to take care of it long term.
Here is what you need:
You need 6 quarts of AMSOIL 5W-20 Signature Series 100% Synthetic Motor Oil ALM-QT which you can learn more about here: AMSOIL synthetic motor oil 5W20
You need the AMSOIL nano fiber long life oil filter for your truck which is: EAO34
Back to AMSOIL for F150s