Can I use GSM and GPS modules at the same time?
Yes.  Use SoftwareSerial for one of them.  That way you can use any pins you like for that module.

I'd recommend using the GPS module on the SoftwareSerial since it's (mainly) half duplex, and SoftwareSerial can't both transmit and receive at the same time like the hardware UART can.

Either that or switch to a different Arduino board that has more than one hardware UART.