So I have a 2004 Chevy Silverado 1500 5.3, about 2 weeks ago I drove to Michigan from Texas and when I got there I realized I was a little low on coolant so I added some. Throughout the course of the last two weeks I have went through 3 gallons of coolant and 6 quarts of oil with no visible leaks anywhere. Took it to the shop they ran compression tests they ran pressure test couldn't find any leaks. I'm about to take it to the dealer and see if they can figure out the problem but was wondering if anybody would know how I'm losing this much fluid in such a short amount of time? I run 5 - 30 Royal Purple oil and K&N filters. Oil changes done every 3000 to 3500 miles try to take care of the vehicle the best I can so I don't understand what could have happened and apparently nobody else does either. So just a shot in the dark thought I'd ask y'all and see if anyone had any suggestions thank you in advance.

Are you experiencing any white smoke out the tailpipe?
Pull oil dipstick, do you see any bubbles or coolant contamination?

I've got a little white smoke coming out but signs of coolant on the top stick. I did have this build up on the oil filler neck friday when i did the oil change

Coolant ingestion is not good news.
I would not continue to drive the vehicle until it is inspected properly!
Has the truck temperature ever overheated?
Going to have to tear into top of engine, remove intake & see if it is the lower intake manifold gaskets or head gaskets or?
It could be a real ugly mess in there, unfortunately.

That'* a sign the intake manifold gaskets **** itself. Highly recommend you drain the oil out and not drive it until its fixed. Coolant and oil mixed together turns acid and WILL eat the crank bearings causing rod knock or worse, knock through the block.

Repair the coolant leak and I suggest an oil change with cheap oil and filter, run it for about a day, then do another oil change with better oil and new filter.

What the others said plus: Don't let it freeze until you:

1. unscrew coolant pressure cap so pressure can't build
2. drain oil
3. remove old oil filter
4. install new (cheap) oil filter
5. fill with new (cheap) oil
6. run for a few minutes like no more than ten minutes
7. QUICK drain oil again!
8. QUICK remove oil filter again!
9. install new (cheap) oil filter
10. fill with new (cheap) oil
11. run for a minute
12. shut off
13. set cap where it is supposed to go but don't screw it on
14. let engine cool completely
15. screw cap on all the way then unscrew one full turn
16. take these steps you did and everything else you know about it to someone you trust to get it diagnosed . . . and yes probably lower intake gaskets based on everything else you ruled out already

Why?:

1, 13, 14, and 15: We don't want pressure to build in the cooling system. Then coolant pressure won't push coolant into wherever it is getting into your crankcase (as much). It will still work and keep itself cool etc., but won't build pressure to keep from boiling under strenuous activities which you aren't doing here.

6: Collect a bunch of the remaining moisture in the cheap oil

7 and 8: Get that moisture-filled oil out quick while moisture is still suspended in it

Thank you for your responses, I really appreciate it. I also did a compression test which I think came out good with all 8 cylinders being 135 or 140 psi. Cylinder 3 was 150 psi though. I'm going to get some parts ordered and hopefully mess with it this weekend.

Good luck! Let us know how it goes.