Lack of power

For 2001, ford, ranger- edge, 4x4, 3.0L-V6, 5spd manual trans, 39000 mi. The problem is lack of power, cruising at 40-45 mph. Upon climbing a 3-4 degree incline, I have to downshift to 3rd gear because speed will decrease due to lack of power even though the pedal is to the floor. This is a constant situation. I try to maintain a fuel grade mixture of 87 and 89 octane all the time (alternating every other week). The worst or most significant lost of power is when towing a trailer (approx 2000 lbs) or with the bed loaded with dry sand or gravel (for construction projects) and climbing the same road. In this situation, I can only reach the top using 1st and 2nd gear alternating to keep the rpm in the safe zone, and the speed is only 10-20 mph. Any fixes for this or is this pretty much what I should expect from my truck? Sorry, cab is a king cab, regular bed. Thanks. Oh, by the way, i'm on Guam, tropical climate yearround, and this is my first time on your website, so I really appreciate the savings opportunities you folks are providing us way out here in the pacific. Looking forward to hearing from you. Again, thanks a lot.