2001 Silverado Battery/Alternator

I cant figure out whether or not my battery is shot or if the alternator isnt working correctly. Sometimes my truck will turn over when starting and sometimes it wont if its in direct heat i.e. the middle of the afternoon. This has been going on for a week. Last night everything went wrong and it took a little longer to get it jump started. When the rpm's go below 2k my truck dies but if i keep the RPM's cranked then my truck runs fine. Any Ideas? Thanks

I cant figure out whether or not my battery is shot or if the alternator isnt working correctly. Sometimes my truck will turn over when starting and sometimes it wont if its in direct heat i.e. the middle of the afternoon. This has been going on for a week. Last night everything went wrong and it took a little longer to get it jump started. When the rpm's go below 2k my truck dies but if i keep the RPM's cranked then my truck runs fine. Any Ideas? Thanks

remove the battery from the vehicle and charge it using a charger at 10 amps..for 8 hrs,,then have battery load tested...
I have seen battteries short out...this is something that throws most non electrical mechanics..

with a known good working, charged battery installed check for 13-14volts dc across the battery, with the engine running at normal idle,,..if its low then to be sure measure the output current if possible to see if the alternator can supply 60-70amps with all lights/ hvac on etc...