I am trying to figure out if I have a problem with the batteries or the starter.

I have not been driving the truck much this last winter but when needed it would start.

It is now at the point where I am not sure if it will start at all, it is barely turning over.

The batteries are 8 years old but had them checked today by Les Schwab and they said the batteries are putting out 604 amps each.

The cables are only a couple of years old and were built with 2/0 wire.

The alternator is putting out between 13 and 14.5 volts

The starter is only a couple of years old and worked good up until now.

I cleaned the battery connections last week and then drove 45 miles so it should have been charged up good.

Any suggestions and ideas are welcomed and appreciated

 

How long you let your truck sit without starting it? If you let it sit for long time you should disconnect batteries and put battery tender/float charger on them.

 

8 years old battery its time to replace them. The best battery life span is usually only 5 years. Your Batteries could have surface charge only and when put under a heavy load when cranking over the engine the amps will fall off very quickly, volts will drop off too. Check the battery volts when cranking if they drop off fast to 9.0 volts then it's time for new batteries.

 

exactly what big iron said- if they are normal open cell batt's they wont last that long and "act" good when tested but perform bad when attached to a CTD.
I tested mine by pulling the positive off the passenger side batt, placing it carefully away from any grounded surfaces and see If I could start the truck with just the drivers side- and nope not even a chance. So I dropped 2 new sears Platinum AGM's in and now it starts up light its plugged into 220v! oh, and it fires up perfectly on just one batt now too
IF that doesn't fix ya up, then its time for a New larry b's starter
I see your in Kfalls, I'll be breaking in our new VW Passat Diesel on a trip to crater lake on the 25th

 

Test your batteries with load tester

 

OP, I assume they put it on a load tester to find out it was supplying 604 amps?

I am unfamiliar with that grade of load tester. The ones I use just say good, weak and get out your billfold.

 

I did the load test and it came back 604.

with the volt tester I tried cranking it over and it went staright to 9 volts and then up to 10; so I think it is the batteries.

Also tried the just one battery at a time and they would not even turn it over.

I guess I will have to buy new ones

 

get good ones, AGM optima or sears platinum