The Lowest cost and easiest things to look for before taking on larger/expensive items
Thermostat might be sticking, coolant might need to be flushed (Deathcool...pink/red and when it needs to be changed...it goes south fast), fan clutch (and if so, there are three levels...OEM, HD and Severe Duty...get the SD) and as noted by others, check the radiators for debris (all three, main ENG coolant, AC and AFT.
Also, the ATF might be in need of a flush, but if it has been neglected...the fresh fluid might loosen up some varnish to ruin the tranny. So take our time checking into that area
{edit}...do NOT open the radiator cap to check coolant fluid level. Use the over flow bottle. It is translucent and check the level there. Air (O2) and Deathcool do NOT mix well
