How to ask for raise?

So I worked for my current employer for awhile before I considered getting my CDL. After being interested and getting my CLP I drove part time for acouple months with another driver. After getting my CLP I continued only part time driving after getting my CDL. This was untill I became a full time driver 4 months ago. I stayed at the same pay even though I was promised a driver raise once I got put on full time. A month passes, I ask when I should be expecting to get my raise. Boss tells me they will ask superior if they can get it done. 2 weeks later they say it is done, I sign paper just to find out that it was not full time driver pay, just a small raise for having my CDL. I asked when I will get full time driver pay and he said it will be acouple months when evaluations come up. 2 months go by (2 months ago), I ask when the evaluation is and he said acouple months again. I found out that isn’t untill June… All this to say I want to demand a raise and say I’m quitting or gonna start looking if I don’t get the raise. Thing is, I’m not sure if I should because I’m already planning on possibly leaving soon (about 2 or 3 months)but for the time being it would be nice to get that extra $4 an hour. Idk what I should do or say. What would yall do in this situation?