1999 chevy 1500 cranks but won't start. Have good spark.

Kelly, could be a few issues, security lock out, crank sensor, fuel pump fuse/relay, faulty new pump,faulty ignition switch, etc. Attached links may help you diagnose the crank no start issue you are having.
Check the attached links,video,instruction and guides, Good luck
"I hope this helped you out, if so let me know by pressing the helpful button. Check out some of my other posts if you need more tips and info."
96 98 Chevy pickup cranks but won start first steps
GM no start no fuel troubleshooting
No Start No Spark Cranks OK GMC Jimmy S10 Blazer

Distributor likely. How many miles ?

Well the ignition system could, and I guess the ignition switch could too.
Are you getting spark to the plugs ?
Fuel pressure ?
Is it cranking and not starting ?

OK WILL CRANK, CHECK FUEL/SPARK AT COIL AND AT PULG. IF YOU HAVE FUEL PRESURE AND SPARK AND STILL NO START.CHECK COMPRESSION ON ALL THE CYLINDERS. THIS A EASY ENGINE.

Has the check engine light come on at all ?

starter is probably messed up or the battery is low cars do weird things when the battery is low

No. You should have spark when cranking. You are checking for spark at the end of one of the wires?

Check your crank sensor down at the bottom right of your timing cover.
Make sure its connected, make sure its clean and doesn't have some metal shavings on it.

the back firing sounds like to me that the spark plug wires are not in right position on distributor cap, firing on wrong cylinder, did you remove distributor or distributor cap?

check your 10amp ecm fuse