This is probably a read/modify/write issue. Try the following:

ShadowC VAR byte

ShadowC = PORTC
ShadowC.3 = 1
ShadowC.2 = 1
PORTC = ShadowC

You can use manipulate the individual bits of the TRISC register directly if you wish. For example:

TRISC.3 = 0
TRISC.2 = 0

Will work just fine.