I have a 1998 1500 4x4 with the 5.7 vortec & factory tow package (separated battery for the towed vehicle). It doesn't like to start when it is hot, doesn't want to turn over. I have replaced batteries, alternator and starter. starts ok cold, but after it warms up it barely cranks over. Luckily its in pretty good tune otherwise so it usually catches on the first try, if it turns at all. The engine battery in it now is only a couple month old and already the rig is back to not wanting to turn over especially when warm

 

Welcome to the forum. It could be the battery cables. Follow the thick red cable from the battery to the starter motor and carefully measure the resistance across the battery positive terminal and the corresponding terminal at the starter. Then, carefully measure the resistance across the battery negative terminal and the engine block. If there's measurable resistance in either, you found your culprit.

 

You said you put a new batt in and "now it is back to starting hard" did the new batt help for a while?

 

Well, hard to say. sorta. Just like if I throw it on the charger and start it dead cold. Cables makes sense, they are down near the heat and more heat means more resistance. I had a buddy with a 99 impala, same motor. He had a similar issue he said it was engine timing. didn't make sense to me but maybe on the newer 8's it could?

 

The timming is going to be the same hot or cold so I would doubt that is it. If the batt is not big enough would cause this. Make sure the CCA is what is recommended for your application.

 

sounds like the problem i have been having, but it fixed somehow when i was adjusting the battery connectoin, i think it was corrosion for me but for you it sounds like you have a short. So like Einst said i would follow the cables and check for any resistance or any spots where bare wire is making contact with another metal surface. this would be in your positive cable most likely in your case

 

thanks folks. I'm thinking the battery cable makes a lot of sense. esp. about the not cranking when hot. heat=more resistance. This is probably really hard on the starter, voltage drop is bad for dc motors. I know this from being a carpenter. a smart fellah gets the biggest gauge extension cord he can for his saws, or they burn up faster.
I'll let ya know what happens.