Mere naaqis khayal mein...a 100kg bumper shouldn't really have made a huge difference to the ride of a Hilux.
SK is spot on about desi pattay. They'll make your ride hard, bumpy, and unnecessarily "frisky" when you drive your vehicle unladen. Adding two pattay is pretty radical stuff...and I can understand how your ride has changed.
I had a similar problem with my FZJ pickup. Because of stiff rear leaf-spring suspension it was pretty bumpy, and there was a huge amount of wheelspin each time I'd start to floor the pedal. I added a metal checkered plate (about 75 odd kilos) a couple of seats (25 odd kilos), a spare tire (30 odd kilos), a roll cage (about 150 kilos), and a custom bumper (about 50 odd kilos) to the rear of the pickup. Now, it's perfectly fine. The ride is nice and "settled" and the wheels don't scream each time you take off.
The point given by qwertpoiu is very pertinent, too. If you're not going to lift heavy loads...stick to a more "middle of the path" suspension setup.