I really need some advice. Some background info first. My Dad passed away in August of 2012 and I wanted his car,even though he had issues right off the lot with it.
3rd generation Nissan Altima 2.5 4 cyl SL
I got it in Sept of 2012 with 130,000 miles and have just about replaced everything (EVERYTHING)except major parts such as Engine,Trans and Exhaust system. 
Now in 2016 it has 171,000 --I am having issues with no heat/windshield defroster,as well as a Revolution problem. It is winter here in USA and I need the heat  
Here is the weird part:it seems to work perfectly only when I'm driving and at 40mph-60mph???

The issue with the Revolutions is fairly new. I have replaced sensors to try and get my SES light to go out. Could that be related? When i drive and let my foot off the gas to coast the car juts forward a little with the Rev needle jumping.Other blogs say maybe the TCM sensor or a reprogramming of the ECM might get it to go off.

Mechanic says bad CAT because of the po420 but I say no,most likely the MAF sensor (replaced recently with Bosch OEM) because it's not red,nor does my car smell of exhaust. 
Any input would really be appreciated. This car has sentimental value to me. We picked it out together back in 02 and my Dad let me drive it off the lot with 5 miles on it 
Please help