Problems with modified xb
 

Ok so I have a 06 xb and I bought it from a used car lot and it had 78,500 miles on it and now it's at almost 95,000 and I'm the 4th owner of this car. Worked great and did 0-60 in 9.98 seconds its has a muffler delete a aem cold air in take that's is modified. Interior it's has viper remote system pioneer navi and DVD player. Exterior lowered trd struts and springs and 17inch wheels I bought like this all I did is do the muffler delete and reroute the intake. And I financed it for $10,450. I've almost had it for 10 months and it now does 0-60 in 14 seconds and the transmission seems to slip on the first and third gear(it's an automatic) third gear hangs a lot and the engine bay gets very hot very quickly. I do tend to drive fast a lot and sometimes push it to the limits when it seem fine. Before this one I had another 05 xb that was stock and seemed to be faster then the current one. All the fluids kept up and I try to take care of it as best I can. If I'm at a light I can floor it and it seems to have a few seconds Of a loss/ very little power then it goes like normal and it seems to get worse over time. And problems keep grow and popping up at random. Ive replaced the battery twice within the 10 months I've had it. If you have any ideas on what's happening and what I can do to fix it please I'm all ears it's more a projected car then a reliable one and it's costing me almost half of what I paid for it to fix stuff. I've had many people tell me that the trannys going out and the cat needs to be replaced any advice will help thank you