kikkup

Hey guys, I'm new to the forum and I am having an issue with my 1998 Suburban that I just bought recently, When You take off it seems to act pretty normal except it seems to shift a little quick ,Like 2000 rpms but once it gets in od,You can feel it bump if you are running under 65 to 70 mph over that it seems smooth, So I started leaving it in drive or third gear when I was running around 45 to 60 mph, And I noticed that when I'm running under about 2000 rpms it bumps in 5rd gear too, Just wondering does that sound like a transmission problem or a converter problem or what ,I'm dazed and confused with these newer tranny's and would really appreciate some help...Thanks Steve