hi fly n fish , i may be able to help you here, i run a 4.5t mod motor in my t4, i dont run in mod class because i run it in a class we have at our local club called 235mm outlaw 1/10, effectively mod cars with no body or tyre limit meaning wide foams and lola bodies, The cars are under high stress due to excess traction and an ability to mash the throttle nearly everywhere
Now mod cars will chew the belt faster then then stock classes but you should still get 25 plus battery packs per belt if all other factors are correct, trust me i have been in your situation snapping belts every 2 to 5 batteries but the good news is there are ways to make it last.
Firstly pulleys and gear diff teeth are critical, worn teeth give you no chance a pulley doesnt need to look chewed out, if the teeth are smoothed out at all they will contribute to poor belt life, pulleys should be changed in a mod car every 10 to 15 packs, a tip here to maximise cost saving is when replacing this pulley put it on the front belt pulley as this pulley is not as critical , this way you get 20 to 30 packs per pulley, now i see you have the aluminium pulleys and while i have no experience with them so i cant be sure, it must be harder on the belt then plastic but in saying this it is still better then a worn plastic pulley so experimentation is the way to go here, also the gear diff teeth that are worn or damaged will also wreck a belt quickly, luckily these last far longer then a pulley maybe up to 100 or more packs but worth being aware of.
belts that get chewed out are generally to tight and belts that snap are generally to loose , i was given some good advice on this and was told to have approx 3 mm flex in the belt when pushing down in the middle of it, this has proven to be very good advice for me and my belts last longer because of it, check your belt tension regularly as well as the belt will stretch.
lastly belt choice. unfortunately Xray belts are a rip off
, sorry guys for being so forthright or offending anyone but the cheapest i have ever found one in a hobby shop is $ 18 while the highest was $36! , this is no good but once again there are solutions, number 1 is don't use rubber belts make sure they are kevlar, i have used the TOUGH racing belts from korea for a third of the price delivered as long as you order a few and they are pretty much as good as genuine, another belt i have tried is a 5mm 189mm team magic nitro belt which i carefully cut in half too create 2 x 2.5mm belts , i snapped one within ten packs but the second one has about 15 packs old and still good, not bad for $ 14, also i have heard that the yokomo belts are better then xrays belt but i cant confirm this as i have never tried.
check all these things out and i am confident your belt problems will cease to be solved
cheers
oldenuff