I have a 2002 Sienna. The transmission was rebuilt at 85,000 miles. I now have 100K and seemingly since the rebuild I have this problem. When the van is cold or has sat for 4 hours, upon taking off, the van feels like it wants to stay in first gear for about 1/2 mile staying below 30 mph. After something heats up, the problem goes away, shifting normally for the rest of my drive. I can eliminate the problem if I start the car and let it warm up for 5 minutes. I've had it back to the transmission shop several times now and they inspect and say it is not a transmission pr:sosadblem.