If you cant get kills with the M4 Sherman with the 75mm then you're doing it wrong.
FIRST... and this goes with ALL tanks, NEVER leave the motor pool with at least the minimum load of HE. Regardless of the AFV, always take some HE. Why? Use HE vs any and all of the lighter skinned vehicles because you dont have to hit them to destroy them. The splash damage will blow tires and throw tracks, damage turrets (M18!), and I've never had a hit on a M3 with an HE not destroy it. You can hit an M3 with an AP rounds and unless it is the front 1/2 of the chassis it passes right on through with no measurable damage. With a hit from HE it goes boom. The M4/75mm (and M3 Halftrack 75mm) has the 3rd best HE in the game behind the T34/85mm and the Tigers. Shot for shot goes to the T34/85 and the Tigers, but throw in the much quicker reload of the M4/75mm and the the longer the firing goes the more in favor it goes for the Sherman. Of course, this is more for OBJ, but I'd much rather be in an M4/75 vs an M18 than any of the power house tanks. One shot of M4/75mm HE and its over for the M18, direct hit or not.
Secondly, play to the strength of the tank. The strength of the M4/75mm is the reload (and the HE). Stay hidden, be patient, and do what every other Sherman 75mm did in WWII: not be alone. The M4/75 can hold its own vs Panzer IV's believe it or not. While the Panzer IV's gun has vastly superior AP ability shot for shot, their armor is very similar. Vs other tanks, it imperative that the "shoot-n-scoot" game be played.
Oh, and I'd love to see the Churchill with the option of different main guns like the Panzer IVF does. They could have both the 6 Pdr with HVAP, and the 75mm like we already have. The speed thing might be an issue, but maybe HTC could figure out a how to put the Churchill on the train and ship it out halfway to the enemy spawn point.
Cheers!