1995 Chevy blazer ls 4 door 4x4 4.3l

Blazers speedometer recently started being inaccurate rises real slowly and goes down real slowly would say that it's about 10mph off . Another thing I noticed is that my idle is a little higher. Usually would idle at 700 warming up and after being warmup. Now warns up at 1000 but then after driving it will go down to 700. Noticed that when I get up to about 30 mph my rpms will rise fine but when they drop they tend to get stuck around 1200-1500 making me unzble to coast or slow down withou braking .I feel like there's there's something wrong with my cruise control or something like that any responses would be greatly appreciated thanks

 

A couple things may be the culprit:
Vehicle Speed Sensor
Throttle position sensor
I'm sure there are other possibilities too, but the VSP would be a good place to start.