Fan in radiator

Check the top radiator support bars that go to the fire wall. And check the rear engine and tranny mounts. Also measure the distance between the fan and the radiator.

Also, when you say you replaced the fan, do you mean the blade assembly or the fan hub assembly?

 

Is the fan hub worn out? You might have to check with engine off, key on as most will exhaust the air and engage the fan clutch with key off, eliminating the bearing play.

 

First, what kind of truck?

 

I don't know if this is your issue, but it is very common. Aftermarket radiators come with a lower bracket that has offset holes that put the radiator 3/4-1" closer to the engine. The OEM bracket has holes centered (front to rear). I usually swap brackets, or if that's not an option drill new holes in the correct place.

The lower part of the radiator is pretty close to the frame brackets, but you should be able to get a finger in there. If it's tight, it's too close. Many times this works, but I've seen many fan kiss the radiator on the lower 1/2 of the fan.

 

Years and years ago, a crazy farmer I know, went to work for the spring at the local co-op.
Everyone had trouble shifting this one truck, well, Crazy John marched up to it, spouting off about how you had to get your rpms real high to shift it.
Before he got out of the yard, he had the fan thru the radiator.

 

Here's a picture of what I mean when I mentioned the wrong lower bracket. On the right is a new aftermarket radiator that I'm about to install in a 2001 379. On the left I'm holding the bracket that came off the old radiator that I will be putting on the new radiator. If you notice the location of the bolt holes, the new bracket would put the radiator closer to the fan, I'm not going to let than happen.