Can I swap my 4l60e for a Th350/400?

[400sbctruck]

At worst youll get a code. Earlier th400-kickdown cable later some electronic(by this time it was th375b/standard in trucks). Go with 375/400 and probably flash shift duties out of ecu/pcm. Vacuum shifted them all and kickdown was main diff.
Really savvy programming guy may put different settIng in your pcm to allow use of 1988-1992 th375b trans later of which was electric kickdown.

If this is for power handling i would take 375b although 700r4 can do good with few upgrades such as the covette servos etc. Main performance difference would be 1-2 gearing difference, as 375/400 is steeper off the line.