97 Ford Ranger No Start Problem.

My Ford Ranger is not starting. It started
up the other day no problem, then when I
got to my work parking lot the engine died.
I tried starting it up again immediately and
it would only crank and not turn over. The
lights and the dash were all normal. Later
on in the afternoon I tried to start it up
again and it turned over finally but only for
about a minute then the engine stopped.

I took my battery to the autozone next
door and they said it was a good battery
(I'm skeptical because I bout it about 3-4
years ago)

I got it towed over to my mechanics and he
couldn't get it to start up the next day but
the other guys there managed to do so and
the problem never occurred again for
them. Finally I picked up my vehicle after
hours after the mechanic said they couldn't
find a problem why it was doing that to me.
I asked them if maybe it could be my
securi lock because I had to use one of my
spare keys after I was locked out the other
day and I foolishly attempted to start the
engine with my old chipped key that Id
forgotten was a different lock profile. They
said it might be the case the truck is now
in Anti-Theft mode.

I picked up the truck because they couldn't
find a mechanical problem that they could
work with and it was running normally for
them. About a quarter mile after I left the
shop the truck died again and I had a
friend help me tow it back to the shop
where it is now until tomorrow.

My question is, has anyone dealt with this
before and resolved the issue, and how?
I'm at a loss of vehicle now so I'm open to
suggestions or opinions.