My gas furnace will shut off before it reaches the desired set temp. It will turn on and it will ignite... runs for about 3-4 minutes and then the burner will shutoff and then it will re-ignite after a minute or two. The unit will run and then the whole systems shuts off. Then after about 5 minutes, the system kicks on and it does the whole thing over again... Any suggestions on why it's not staying on until it reaches the temp?

Hi Lisa and welcome, does the fan start? Is your filter clean?

Remove and clean flame sensor. Clean with something like kitchen pot scrubber and soapy water, Rinse and reinstall. Do you know what flame sensor looks like?