What do these do?

 

depends on the application. on 1993-earlier 4L60 trannys were not electrinically controlled so you had 2 mod the valve body in the tranny to let the ATF flow correctly and they increased the line pressure for shifts. in 94 the general made the 4L60 electronically controlled so the computer set the shift points and converter lock up not mecanically anymore so you have to modify the computer settings to really see any performance increase in the automatic