2000 Ranger runs hot on highway

The truck's a 4x4 Off-Road 5sp, only non-stock item is a set of 32" mud tires. Around town the temp gauge stays right in the middle. After a while of running on the highway, it starts to climb towards H, though it never gets all the way there. Usually I run with the heat on to ensure it doesn't. If I slow down it will usually bring it down a little also. Not sure if this is a huge problem or not.

I've been wondering if it'd be worth it to get a CAI kit before this anyway. Do you think one might keep the temp down a little?

Add some Redline Water Wetter to your system. It can decrease the temp by up to 20 degrees.

it would be advisable to flush youre system and maybe replace thermostat to ensure everything is working correctally. watch water flow in radiator cap to see if water pump is flowing water through everything.check hoses to see if both are warm wich will check for any blockages.