1993 Mercury Villager Shifting

The van shifts hard until it warms up, then it runs and shifts fine. If the van sits in the sun for a while it will shift fine. Checked the fluid level its good. I am planning on replacing the transmission filter and gasket to see if that helps the problem. Have also been told it might be the bands in the transmission causing the problem. Which is the most likely culprit causing the hard shifting and jerking, the bands or the filter?
Also, during the summer, (we live in AZ) the van will run fine until it gets to operating temp then it will lose power and die, we sit and let it cool down and repeat the process. We put some pipe insulation on the fuel line under the hood and pour water over it on hot days and we have less trouble with it. Is this a vapor locking problem or is there a problem with the fuel pump? I have been told it could be either one. We don't let the gas tank get below 60 miles till empty because it seems we have more trouble with it getting warm and dying. I hope I explained this well enough for you to understand.