Transmission shuders at 40mph to 60mph

If it's a automatic check to see if your torque converter is out of balance that sometimes will occur in a automatic transmission

Could be a tranny problem developing but cheap checks include checking uni joints or cv joints for looseness. Check rear bush of tranny for sloppy slip joint fitting ( rear drive only) lift tail shaft up and down. any movement allows an out of line tail shaft to occue hence the shudder.Check the color of the tranny oil Should be a bright cherry red. Any other color ( brownish red - tan) indicates possible tranny fault