Good morning, thank you for the help with the comments. My truck was runnin fine till this mornin. I was drivinin up a grade and got a power loss, i had a small load of wood on but have pull this grade many times. i had to sift to 3rd. which is not unusual, but then i had to shift to second, which is unusual, on my way back, i went up the same grade, same thing, never had to go down to second, i was unload, i coulds still feel it. it feels like to me, when the truck is in third gear, almost to the peak of shifting to forth [about 40 mph]the power drops or almost feels like it bogs. When i do shift into forth, i can feel it again and if i give it more gas to pick up the speed, it bogs and there is a vibration. My truck is a 1983 Dodge Ram 50, 4x4. The Motor is a Mitsubishi, Model # L026, Engine # G63B, 2.0, 4 Banger.Thank You for your time and any help.