I had the same problem on my 2001 Chevy Tahoe, the rear heat worked fine and the front heat was barely warm. One mechanic said I needed a new heater core for $1500, but I took it to another and asked them to reverse flush the coolant system (under $200). This worked great and the front heat is back to working again.

 

01 tahoe my heat works in the rear but not the front panel any knowledge helps

 

I would guess that one of the three actuators under the dash is malfunctioning, not uncommon. These operate doors or flaps to direct the air. Since heated coolant is what produces the heat, does not sound like an engine issue at all since you get rear heat.