G’Day Michael, with what you have said there about T-Con gage being near the red & light on, this tells me that light & gage seems to be working fairly correctly. If you are working in 1st gear when this is happening & T-Con isn’t in stall conditions I would suggest you do the following.
• Get T-Con outlet relief valve pressure checked, spring can become weak & allow lower pressure which can cause overheat.
• While getting this checked double check your gage against a master gage just to make sure.
• There is a screen in the bottom of the T-Con on the suction line that goes to the trans pump, check this.
• Before checking screen above, do a T-Con stall in 3rd gear with foot on brake till temp comes up, let idle for 30 seconds or so, shut of engine, remove hose & drain T-Con into a bucket. There shouldn’t be a lot of oil, rule of thumb 2 litres max. if more T-Con seals are leaking causing it to flood & generate heat.