Oil....

My 1999 Tahoe has a 5.7L engine. What weight oil is suggested to be used? I've heard that no matter what oil is suggested, that you should use 10w-30 in the winters and then 10w-40 in the summers because it holds up to heat better. What is everyone's feedback? Are there any prefered manufacturers?

I run 10w30 year round in my 94 K1500 5.7L and in my wifes 02 S10 Crew 4.3L. I use valvoline, castrol gtx is also an excelent oil. For synthetic oil I would use Royal Purple.