no3pike,
To get an accurate voltage reading on any battery you must let the battery cool down. If a reading is taken immediately after charging, the voltage will be higher than actual as there will be a temporary surface charge that is being read by your volt meter. FYI you will greatly reduce the useful life of a battery by operating you lift immediately after charging - the battery is hot and has yet to reach full voltage capability you maybe be running under voltage. A rule of thumb for industrial batteries is it take 8 hours of charging to fully recharge a battery that has been discharged 80% then 8 hours of cool down time to allow all cells to reach ambient or room temperature, especially the inside cells, the 8 hours of run time.
Another rule of thumb is new batteries have X number of charge cycles in them from day one - some people say 1400 others say 1800. What every the number is a charge cycle is any time you hook up your battery to a charge counts as one charge cycle whether the battery is on charge for 20 minutes or 8 hours. During the start up of the charge cycle, the initial charge amp rate is near max charger capacity let's say 865 amps or greater. The reason for this is to clean off any sulfate build up on the battery plates so full charge can realize. But at the same time a tiny amount of lead is removed from the plates & settles down to the bottom of the battery and stays there. Over time this lead can build up and create a dead short between positive & negative plates - bad news - a battery cell needs to be replaced = $$$ spent. So by frequently doing what you have stated you have or are now doing (charging for 45minutes run it, charge it again, run it you are further shortening the life of this almost dead battery and doing harm to your truck.
Don't feel like you are the only person on the planet that has done this. I have have seen too many case of the same symptoms as you have described that I think a Hotline for reporting ABUSED BATTERIES needs to be established. But the lobbyists for the BATTERY REPAIR guys have been able to stop it.