2004 Kia Sorento hard shifting from only first gear

I'm getting the run around from KIA. Problem is when COLD the car is extreamly hard to shift from 1st to 2nd. All other gears are fine. You have to almost yank it out of first into second. I was first told it was. Ready.A dirty trottle body as the transmission computer check told them that. Of course once I told them to go ahead and clean it BUT I would not pay for it if it did not fix the problem they backed off. Now they say it is the clutch. I'm 56 years old and have only had one car with an automatic in the 40 years of driving. I have always had manual trans. There is no slipage at all and again the car shifts fine through all the other gears. All the required maint. Has been done on the car by a certified mechanic at a local shop on time. He feels, as I, that this is a transmission problem that should be covered under the warrenty.