UART Communication between GSM and GPS

What GSM or GPS module are you using?

I do not understand the part where you say the GSM and GPS should communicate with each other. Normaly a microonctroller is used to communicate with these two modules. 

I am using the interpreter of the telit gsm to process the data recieved from the GPS

Did you check for baud rate? Your GSM modem and GPS should work in same baudrate for them to talk to each other.

Provide part number for both, this will help people understand what hardware u r using 

Hello...as per my knowldge GSM modules usually has output with 1.8V (for example VAUX/PWRMON on Telit LE910), ypu could use it to power level shifter ic.Not sure about GPS module though. Specific part number would be helpful

To setup a communication between two communication modules or a module with a controlling device, you need to check the baud rate requirement of the modules, from their datasheets, as most of the modules have communication at 9600 baud rate. And for logic level shifter, you can use any logic level shifter to maintain a specific voltage/logic level for both the modules. Here I would like to suggest you SSLA, for getting assistance in your project. Many times, I got assistance from them in my projects.

Check the logic levels of both devices, if they are working on different logic levels, then use a logic level converter.also check if they are sharing same baud rate for UART communication or not.

As pointed by others, check the baud rare and use a level shifter.

For example you can use

https://circuitdigest.com/tutorial/bi-directional-logic-level-controlle…