What would cause my 95. Chevy truck to start And run briefly then shut off.good fuel good spark

The first thing I would check it the oil pressure switch. I think it has two. One by oil filter and one by distributor. It's been a while since I have worked on one but I remember their being a problem with one of them to make the truck do what you have going on. I would first look at on by distributor

Checked them already but thanks

Ok well do have means to check the fuel pressure ? See if it goes away to make engine stop running. Can you keep the motor running if you give keep it above idle. Or is it like you are turning the key to the off position.

Runs above idle if you keep hittingnthe gas but very rough.cut off as soon as you stop pumping the pedal

Just going to throw this out. It almost sound like you have a big vacuum leak. Check intake boots very close for a tear. Then try unplugging the mass air flow. Not sure it that year has one but if it does try it. See if it idles any

Did that first

Wow just forms shits and giggles I unplugged the map sensor vacu um again and Its running fine?sprayed the engine with carb cleaner and can't find any leaksin vacuum though?

You put a new map on it ? If so, has same problem with old sensor ? Almost sounds like you got a bad new map sensor

She idles OK but still won't run in gear I might try another. Map sensor