2000 B2500 no heat

I've checked other threads for the ans before I post any questions.2000 B2500 4cl no heat. The temperature gauge is acting funny it wasnt working at all before I put a new heat valve on, thermostat, and topped off with a 50/50 antifreeze mix.Now the gauge will read it's warm but no where near over heating.It's blowing soso warm air nothing to brag about no antifreeze inside cab the radiator was flushed and old antifreeze looked muddy .Is it possiable the core can be clogged? all hoses feel warm like there suppose too.Any ideas?????????