Why does truck want to turn off?

I was at the drive thru at mcdonalds when all of a sudden the truck (04 ford ranger) started trembling then turned off. I freaked out and turned it back on. It turned on with no problems but then started the whole trembling thing again so I got out of line and parked. I'm currently parked and the truck is in a cycle of going up to 1k revolutions then slowly going down to 500 revolutions then almost turning off then shooting back up to 1k revolutions. What's the problem? Is the engine shot?

Should I keep my truck?

I have an 86 Ford Ranger and it just hit 350,000 miles. It is my daily driver and my weekend warrior. I love this truck, but she is starting to have problems, the biggest of which is there's a small crack in the head. In total everything that I need to fix will come to about $2,000 not counting another $800 for new tires. I'm trying to decided if it is worth it to fix my truck or if its time to move on.
I'm just out of highschool and only work part time so I don't make alot. Also I love this truck, its my first vehicle and it has a lot of sentimental value to me.

Excess steam (White smoke) and water coming from my tail pipe?

Okay, I bought a 1996 Ford Ranger 6cylinder 4.0 XLT truck about a week ago. The guy knew something was wrong with it, figured since I was female, I couldnt fix it… Turns out he may be right. I took the motor apart down to head gasket, but didn't actually change the head gasket. I cleaned everything up from the oil, but hated the thought of having to go into the head gasket. However, days later, a new intake gasket, thermometer and coil pack later, I still have this ridiculous amount of water and steam coming from my tail-pipe. I'm hoping its not the head gasket but wondering what ya'll think. Before you ask, the motor runs and starts fine, the oil is not milky. I'm thinking the vehicle has the original spark plugs (Plan to replace those when I do the combustion test when i change those), but not sure if that would even effect the water in exhaust issue.

Added (1). The motor does not overheat

The water (Radiator fluid) does go down

It IS steam, not oil smoke.

The intake gasket was not torqued properly, could a warped intake cause this issue?

How do I properly test a bad head gasket?