Why does my transmission hesitate to shift, and later to slip out of gear and rev up?

What is your question?

Several days ago, the transmission was shifting "late", with RPM higher than normal, on the first several minutes of driving...the weather was over 100. The flid level is good,but today started "slipping". When this happened on my last two Aerostars, the trasmission required rebuilding soon thereafter. Is there something I can do to avoid another transmission-ectomy?