1991 Chevy S-10 can get it to start

Start with the basics, and work your way up, Last tune up was? Wires plugs ALL filters? If all that is ok, check for a stuck EGR, then test fuel pump pressure, If it won't restart, determine what's missing, the engine needs three things to run, Spark at all plugs, gas to all cylinders, and compression in all cylinders, tho an engine may run lacking one in one cylinder, it won't run very well!
https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
https://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm
and this one!
When you say it has trouble what kind? Clicking? or nothing at all? If you hear a click, then either the battery is weak, or the starter, possibly bad battery cable connections, check and clean both ends of BOTH cables! Dissconnect negative(-) first, and put it on last! If no click the starter relay is no good!