Sometimes my ABS and Break light will stay on nothing. Nothing seems out of the ordinary. What would cause this?

check the brake fluid level, or could be the abs module

ABS sensor my be malfunctioning. Don't try pulling the ABS fuse to make it go away. Don't ask me why I told you that.

abs malfunction,need to get the code to know what is going on.

It may be a common problem for the year model as mine does the same.

A very very common problem. Look at ebay for ABS control module. They will tell you how to remove and send to repairs.

How much is the ABS module?

My 99 GMC has the same problem.

David- Search the internet for "ABS and Brake Light". There is a company that will recondition the module for around $100. Otherwise they are around $1000.

But as Stan mentioned, you will more than likely need the codes pulled.

Try this link

http://modulemaster.com/en/index.php

+1......we use them all the time....good work and fast turn around time

Will the truck operate safely without the module?

Not sure. I would expect the brakes to still work, you just would not have ABS. I do know if the brake light is on you will not pass inspection.

David you will still have base brakes,just no antilock brakes and no traction control,the brakes will not stop in the same distance they will with antilock because the antilock system incorporates a pump to boost pressure to the brakes.And as noted with any type of brake light it will not pass inspection.

Last has not come on in a couple of weeks. Next time it comes on I will get the codes ran.

David #1 I would be suspect of a bad wheel speed sensor. especially since you say it appears intermittent.
base brake/abs lamps are a confirmed fault that disables abs/tcs.
pull codes to verify. front will have to be replaced, but are available w/out buying the whole damn bearing asm now.
rear unbolts from top of Diff, and probably needs the
metal "goo" cleaned off of it.
disconnect battery before performing work. seriously.
bad module has become a go-to thanks to the internet.
not nearly as failure prone as internet suggests.

Is your truck a 4wheel drive? If it is the first thing i would check would be the front wheel hub bearings....very common on 4wd. If thats not it my next guess would be the ABS module...will prob have a CO265 ABS code in the ABS if the module is faulty.

ABS module...had the same issue with 2001...along with 1000 other issues. I have had more issues with this truck than I care to talk about. Not very happy with GM.