Was pulling a trailer with another truck on it some months ago and saw a bunch of grey smoke coming from under the truck as I came into town after some mild hills. No noise or change in driving, just smoke. No smoke since then. Transimmsion fluid seems normal (level, color, etc.). Engine oil...same.

But, when the truck is cold, if I get above 1500 RPM, there's a squealing noise coming from somehwere. If I slow back under 1500 RPM the noise stops. After driving a bit the noise doesn't happen at all. Once the truck is warmed up there is no noise above or below 1500 RPM.

I know RPM is engine-related, but It doesn't change tone or pitch above 1500 RPM so I don't think it's an engine problem. My question....what happens when the torque convertor/transmission hit 1500 RPM input?

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1998 Ram pickup, 5.2L, 46RH/46RE transmission (I can look closer if it matters), 4x2

 

Have you checked the belt?

 

Serpentine belt, belt tensioner and/or something driven by the belt that's possibly starting to fail (water pump, alternator, power steering pump).

 

Definitely put a wrench on tensioner and make sure it springs back with authority. I've seen one just kinda "freeze" such that where ever you set it, it would just kinda stay there but that can't provide honest tension