Possible Transmission problem

I have a 2002 Ford Explorer XLT, V6 4.0, 4WD, with approximately 94000 miles. I'm afraid I have a transmission that may be going astray! I'm experiencing not hearing the vehicle shift when it's traveling 30-40 mph, then it shifts normally, at takeoff there's a slight hesitation but nothing major and not at every takeoff. I hear no strange noises other than my differential that I have recently been told will need to be replaced. Do the two have anything to do with one another? I attempted to check the transmission fluid but found no dipstick and was told it needed to be put on a lift to be checked! How convenient. Do you have any advice to put my worries at ease? I have read through the questions and notice in most cases you've recommended a transmission fluid change I sure hope that's the case! Thanks in advance.