Gets a little hot at 75 mph or more.

Ok, so maybe I just don't need to drive over 70, but I tend to expect all my vehicles to be able to travel at highway speeds, which for me means 79-80. At 65-70, she's just below the halfway mark. Good to go. Kick it up to 75, or especially 80, and then we move up a tick or two above halfway. I read on TVP or somewhere that someone was having that issue, only more serious, and they took off or replaced their cat converter and they were good to go. So I took off my cat. No noticeable change.

So I have three theories at this point.

1) Possibly my radiator is still somewhat restricted. I got it recored several months ago, but my heater cores are really clogged, and I tried to run the heat, so I may have pulled a bunch of crap out of the cores and into my radiator. Remind me real quickly, how hard is a heater core replacement, and how much do they run for parts?

2) My tranny is overheating, and transferring the heat to my coolant. This seems unlikely because my A/T oil temp light has never come on. But maybe the sensor is messed up or something?

3) I assume my fan is probably completely off at that engine speed, so maybe somehow there is not enough ram air flowing through the radiator. At first I thought this was the least likely possibility, but the more I think about it, the more plausible it seems. I still have the A/C junk in the way. The A/C doesn't work, but I still have dreams that it could one day. Maybe I need to let that dream die and get that junk out of the way?

Let me know what you guys think should be my first course of action, and what other possibilities I'm not considering.

I should add the I do have an oem thermostat, but I did get the engine very hot once (I know I shouldn't have, but stuff happens) after I installed it and I've heard that can mess them up. I also have oem rad cap. I have NOT replaced the fan clutch. I do hear a "roar" when I first start the van and take off. It usually cuts off right around 2500 rpm or so.

Thanks in advance for any ideas and advice.

You should hear the fan roar for at least 10 seconds when you rev the engine from stone cold. You should also be hearing it again and feel an associated loss of power before the temp hits the 75% mark (assuming the gauge is accurate).

On a standard radiator configuration (radiator in the front) you don't need a fan clutch while cruising because you get the "ram air" effect. On the van the radiator is behind your legs and is blocked by the floor boards. This restricts the "ram air" and makes the clutch fan much more crucial while cruising. While cruising at higher speeds the air tends to rush by under the van and (bypassing the radiator) and the engine is working harder (producing more heat). Based on what you said I would suspect a bad clutch fan. Tim

Yeah Tim, That really makes sense. I'll see what I can do. Thanks!