hard to shift into gear

I have a 1994 3.2l4x4 rodeo with the 4l30e. when its cold outside, and i start the truck, when i go to shift inot gear it is harder than normal to get it to shift into gear, once its in and runs a few seconds, then it is easy to shift in and out. just wondering if this could be a fluid problem or something to do with the linkage, also the fluid is at proper level. i was wondering if changing the fluid may help this, also could someone tell me how to change the fluid, so that it all gets changed. Thanks
Dave.

could be low fluid. or dirty fluid.

Do you mean that it is physically difficult for you to move the gear selector or that it takes a long time to go into gear?

sorry. I meant that it is physically difficult to move the shift lever. Its not like you have to pull so hard that its going to break, but is much harder than normal. Thanks
also, it shoudnt be low fluid, as ive checked it both warm and cold and its at its appropriate marks on the dipstick
Thank you
dave

Well, if it uses a cable to select the gears (not sure), you could have some gunk inside the cable jacket that gets gummy when cold but softer when warm.