The rpms are running high & won't go above 30 MPH, what could be the problem? on 1997 Chevrolet Suburban 1500

I have noticed a whistling sound, could it be related?

Sounds like the transmissionis is slipping. If so, you need to get it checked out but most likely it's too late for any help. You can check the fluid level and see if it's ok and if it smeels/looks burnt.
1 more answer
I agree with pushrod. Most likely it is the transmission. Not a DIY problem at any rate, so take it to a shop.