If I take out my 1974 Spider (it's SPICA, just like jcgoodlett2's 1981) when it's cold (something like 20 degrees Fahrenheit), and shift into 5th gear when the engine is not fully warmed-up, it will turn off. Yes, it will quit running! The first time it happened, I was leaving work. I warmed the car some in the garage, but not fully, drove for about a 1/2 mile, and then got on the interstate. I brought her up to highway speed and as soon as I shifted into 5th, the car turned off. It would start and idle fine, but as soon as I would start going into a high speed, it would turn off. Once fully warmed-up, there was no issue. I did this twice, and since then I have never tempted fate and have always warmed-up the car fully.... a warning about NEVER shifting into 5th unless the engine temp is above 175 degree Farenheit...
I don't know if my 1974 manual has the same warning as jcgoodlett2's manual, but I will check it and report back. I won't be able to check until the first weekend in December, but I won't forget.