Ok so heres the deal when I first start the car evens out at 900-1000

After driving it for a while and getting on it some(Shifting at 3500-4k rpms) after shifting it wants to stall but comes back up to 300 rpms and sits there and just idles are 300. What is causing this?

Its also running real rich after getting on it some and my gas mileage is horrible right now.

BOV is recirculated

Also will a bad slave cylinder or throw out bearing cause 2nd gear to grind? Its got a new clutch and has recently started grinding but it dosent grind everytime... just sometimes. Or is it the syncros? Trying to save some money... The clutch pedal occasionally sticks but I can pull it back up and keep driving so im thinking thats probably the slave or master cyl?

Info:
95 GST
108k
Head has 20k
2 1/2in Exaust
All stock