If the trans is in 2nd or 3rd gear is the stall locked up? Or can it still be spinning free if under the advertised rpm?

 

When you are under acceleration and above the rpm, it is locked per say! It is a fluid lockup, not a clutch lockup like the 94+ trannies.

 

So I have 2500 stall. In third if I am cruising under 2500 will there be an overheating problem because it won't lock up?

 

Here is an excerpt from wikipedia.

The maximum amount of torque multiplication produced by a converter is highly dependent on the size and geometry of the turbine and stator blades, and is generated only when the converter is at or near the stall phase of operation. Typical stall torque multiplication ratios range from 1.8:1 to 2.5:1 for most automotive applications (although multi-element designs as used in the Buick Dynaflow and Chevrolet Turboglide could produce more). Specialized converters designed for industrial or heavy marine power transmission systems are capable of as much as 5.0:1 multiplication. Generally speaking, there is a trade-off between maximum torque multiplication and efficiency—high stall ratio converters tend to be relatively inefficient below the coupling speed, whereas low stall ratio converters tend to provide less possible torque multiplication.

It is a good article.
http://en.wikipedia.org/wiki/Torque_converter

 

FWIW, the torque converter in the C-4, C-6, et al, is of the non-locking variety. If the OP is talking about the newer cars in the sig, then those trannies lock up, though not in all gears.

 

stall speed depends on the torque the motor is putting out, its not locking up unless you have a non stock tranny in your classic

 

Exactly. Older converters don't "lock" at all.