hey guys.sorry if this question seems dumb but ive never had this happen to me before. was driving home from work when my truck started to act up . felt like the clutch(which is soft and getting old) was slipping at first. but slipping faster then it should. first thought was maybe rear main seal went and oil was getting on flywheel and clutch,causing fast slippage. but engine temp. was fine and so was oil pressure.truck would not go over thirty pushing the throttle all the way down. pulled over and truck died. oil check proved fine and clean. no leaks anywhere. tried to turn it over and all i heard was the starter clicking. put in an old battery and she started...seems to be running fine. volt checker is kinda weak so not sure if it read right. needle for alternator check was jumping around..mighta been my shaky hand...alternator is a year old. sorry about this long diagnosis but would really appreciate the help if anyone has experienced this before. could it just have been the battery going totally dead? or maybe a problem with the alternator or distributor?