1994 Buick LeSabre tranny

I have a 1994 Buick Lesabre with 150,000. I am losing transmission fluid, but there is not apparent leak; nothing on the ground. It is not in the radiator and does not appear to be burning out thru the engine. Anyone seen this problem? I guess my next step is to replace both the pan seal and the main seal. Thanks,

You could be losing it through the output shaft seals. As those seals exist to keep the fluid inside while allowing the shaft to rotate, it would make sense the leak was worse when moving. Thus, you'd be leaving the fluid on the road as you drove instead of the drive way. Beyond that, the fluid would be to the extreme sides of the engine compartment, thus not the place most people look for evidence of a leak. You could also have an internal transmission problem causing the transmission to blow fluid out the low pressure blow off (overflow) valve, located at the top of the bell housing.