Trany won't down shift

Hi I have a 95 astro van the trany does not down shift after the the unit warms up. It works fine when cold. you can manualy shift it in to lower gears but you have to do this at every light! I have just bought this unit, I was told that the heads where just done. could there be a vacum line or wire not hooked up? Thanks for your help

AFAIK, there is no vacuum line to the trans on your van. The 4L60E transmission is completely electrically operated (well, not completely, but there is no vacuum modulation nor TV cable). If the trans operates differently when the temperature changes, that usually indicates an oil pressure problem. The first suggestion would be to drain it and get a clean filter and clean oil in it. Unless it has ridiculously high mileage, and has never had a trans oil change, you can't hurt anything by changing the oil and filter.

While the trans pan is off, and you're crawling around under it, you may want to check the electrical connector on the right rear corner of the trans, and look at the connections at the solenoids on the valve body. You should also measure the resistance of the thermistor in the valve body, since they can be a problem. With the pan removed, you cna also pop the circlip from the pump pressure relief valve and inspect the body and spool, 'O' rings, and springs. Just make sure you get the circlip back in the correct groove (the upper one, not the lower shoulder) when you reassemble the pump pressure control valve.