When the topic of monitoring auto trans temps came awhile ago, there was a more expensive option that looked good, however, they don't make anything for the smaller trucks, like our Rangers.
So, I purchaed the Scangauge II and the BlendMount holder (mounts the ScanGauge II above the mirror) to monitor my auto trans temps via a programable "X-Gauge" feature. However, getting the ability to also see "almost instant" reads on the miles per gallon and an overall, "so far... average mpg", was a big bonus.
It altered my driving habits, when I first got the unit, I was only getting about 16 mpg, now "I'm in no hurry to get anywhere" (the key factor IMO) and the dollars saved have already paid for the ScanGauge II and the BlendMount.
The Scangauge II lets you view at one time 4 data points, so, I've got selected 1) instant mpg, 2) the avg mpg, 3) the numerical value of my water temp (instead of the needle on the dash gauge moving left or right), and 4) the auto trans temp.
I purchased the Scangauge II from Amazon, about $10 less than going direct to ScanGauge, both have free shipping.
The BlendMount I purchased directly from BlendMount and they had a $10 discount (you have to ask them about it) that helped pay all the CA sales tax (they are located in No Cal) and a little of the shipping. At first I was thinking that the BlendMount would be easy to build myself, then I saw one in person on a friend's truck and I thought it was a better quality than I could make.
I'm just a walking advertisement for things that work for me.
Everyone else's results may be different.
I'm sort doing some research, from time to time, on getting a performance chip for the Ranger to see if I can get even better gas mileage, but have not yet got the complete story.