G3 lag and high temperature shutdowns

I've had my G3 since launch and it's always lagged really bad when I've been using more than 1 app at once e.g., listening to music and web browsing. The device reaches 95c and then shuts down so I've had to downclock the CPU to 1.9ghz to stop the shutdowns. With it underclocked, it lags even worse now and still reaches quite high temps (75c~) I'm still on a rooted Kitkat as I haven't had time to upgrade the ROM. Do the new 5.xx ROM's fix the lag? Does it still over heat when doing really simple things?