i have a similar truck, and i bought the kenwood dnx5120, with navigation for about $600, i can assure you, it is a great headunit and the navi is built in, so no mess with the map dvd's.
before i bought the kenwood i was looking at the AVH-P4000DVD, also the avic-d3. my suggestion is buy from any good brand name company (alpine,pioneer,kenwood,eclipse, etc) but get a 2008 model and you will be satisfied.
it really depends on your budget.