would i need to put in a new transmission if my blazer has been sitting in the driveway for like 4 years without moving and hasnt been started and the engine is rusted.?

 

tranny is probably fine, engine might be seized though.

 

trans should be fine.
1st you need to drain the gas and put in new,try starting the engine, if it starts let it idle for 15min to 1/2hr, then shift threw gears with foot on brake for 5 min or so. If it doesnt start pull the spark plugs and spray in some wd40 let sit for 1/2hr and repeat, put in plugs and try starting now, if it starts do the shifting thing. Dont be suprised if it wont move because the brake will probably be rusted.