'90 GMC Van burning oil, check engine light on

We've had a 1990 GMC full size van 2500 (V8. Over 206,000 miles on it) since 2003. It has always used oil & smoked (white/light grey), but never this bad. When we first got it, it was using a straight 30 oil. Then we started using 5w30. Then, we switched to a 10w40. All oils would burn/get used up. Maybe 1/2 to 1 quart a week, depending on how much driving was done. Recently, we got another oil change done and put in 10w30. Then, we went a long road trip. We made sure it was full on oil, and brought a few extra quarts with us. We got about 250 miles out, and smelled a burning smell & heard a tapping sound (lifter tapping?). We pulled over, checked the oil, and it was 2-1/2 quarts low. We put it in. The noise stopped, the smell went away. We drove a little more, noticed that it used another quart. We replaced it (and purchased more quarts!). We drove a little more, replaced another quart, then the van started chugging/losing power on the highway. It only chugged about 4 or 5 times, then stopped, but then the check engine light came. We also noticed that the van was smoking more than usual, plus it was dark gray/blue smoke, plus every time we accelerated, smoke would come out. We drove a little more, then stopped, put in more oil, then decided to come back home. I think we drove around 450-500 miles at this point (so round trip was around 900 miles or so). All the way back home, these symptoms continued (burning oil, excessive grey/blue smoking, & engine light coming on intermitently), with us having to add 1 QT every 60-80 miles or so. What is wrong? Is this something we can fix (is it as simple as switching to a thicker oil. If so, which viscosity?), Or is the engine about shot? Thanks in advance!