I have a 1987 Ford Ranger and sometimes when you start it up (hot or
cold) the engine runs so ruff that it feels like only three of the six
plugs are firing.  The engine shakes so hard that it feels like it's
going to jump right out of the truck.  Then after a while it starts to
run OK.  Sometimes when you come to a stop sign, the engine dies.  It
usually starts right away and runs OK, but sometimes it doesn't.  It
has a manual trans, V6, 2.9L engine with twin gas tanks.  The engine is
fuel injected with electrical ignition.  I keep the engine tuned and
with regular oil changes.  I just replaced the air filter, spark plug
wires and distributor cap about 8 months ago.  Twice I've added
'Heet' products to the gas tanks to get rid of any possible water
in the gas.  Also, added a product to try and clean out the fuel
injectors.  The other day it started and would not take the gas at all
and the engine died each time.  The battery finally died and had to put
it on a battery charger.  The next day it started like nothing was
wrong.  The truck never acts up when you are driving down the road at a
constant speed or slowing down.  Can you please help?
Thanks!   Rocky R.