Its awesome that you got 30 mpg with a 98 Dodge Caravan.
My car doesn't shift at 1500 rpm, the lowest rpm at which it will shift is 2100rpm.
At the beginning of the video, when I shifted to reverse and my foot was not on the gas while I was backing up.
I could get it down to 5mph but I didn't want to, so I just accelerated to around 20mph before coasting. The mpg trip computer always put out a higher mpg number when the car is coasting at a higher speed.
I have read on the internet that cars with automatics basically decreases the fuel consumption to nearly nothing when it is coasting in gear, I was expecting people to back out of their driveways so I didn't put it in neutral.
When the engine is cold just put it in gear after starting and observe when it shifts, do not put your foot on the gas pedal. It will shift on its own and will slowly gain speed. I bet it will shift at a lower rpm than you think. If it does not then you may need to tune it a bit. Check all hoses, filters, vaccum, to get the best performance to get it to shift at a lower rpm. Check your gear ratios to see at what rpms they are supposed to shift. It may seem like a small thing but it adds up over the long haul. Hope this helps.