It's broken

It idles fine, It drives under low revs but as soon as I try go faster than 10 mph it dies!
It ran like a peach before I put her in the garage, & it has done about 50 miles since its last service & there doesn't appear to be a misfire (engine note doesn't change when I pull out the leads one by one)
I think their may be an issue with the temp sensor because as soon as I start it the temp gauge goes to hot & the light starts flashing.
Is this my problem? Has anyone else had anything similar?