This is going back a few years, but the same thing (hard to open, eventually broke) happened to my dad's truck. I got a new inside handle assembly from NAPA (maybe a dealer... don't remember). I think it was about $35.
For the hard to open part (again going from memory), I believe it was the little plastic piece that connects the steel rod (from the inside handle) to the latching mechanism. It was weak/partially broken.
1998 K2500 Suburban 6.5L TD 3.73 rear, Ron Schoolcraft 18:1, Kennedy ECM & IC, Timing gears, Splayed main caps, 3.5" Kennedy Exhuast/No Cat, K&N Filter, Boost/Tranny Temp/EGT(Pre Turbo), Ceramic-coated Manifolds, 195 Stat's, 265/75's (VSSB Adjusted) 7,000lbs (on a scale) Remote Mount Oil Filter, Remote Oil Pressure Sensor