My truck RPM's have started fluctuating while driving it at a consistent speed? 1999 Chevrolet Suburban?

Ok so there are several things that have recently started happening. The first is the RPM's are fluctuating while I am driving at a consistent speed and I can feel the truck accelerate and decelerate as this is happening. The second is that the dashboard lights have started to flicker in and out but are always lit, just different levels of brightness, as well as the interior lights flickering on and off at random times. I now have a huge oil stain on my driveway, and yet my oil levels have maintained normal levels. What is going on with my truck? Are they all the same issue or different ones that just chose the same time to develop? Or is one of these issues actually causing the others?