Dell Inspirion 5748 - WIFI speed drop

This has occurred since day 1, and I first assumed it was win 7 that was the issue but it occurs in win 10 also.  Unfortunately the warranty was up over a year ago.

After power up or cycling the WIFI connection via windows, I have a connect speed of 72 mbits.  This will last for some time like a day or two and then it starts dropping (I think, I have seen medium speeds) and ends up at around 5.5 mbits.  This issue has occurred with three different wireless routers.

Now, my old Vostro 1500 is still chunking away at 72 mbits per second with no issues (XP and Linux) and my daughter's equipment stays connected at 72 when she is over. 

I have been through the dropping threads, but what changes I have made do not affect my issue.

I3-4030U and Broadcom 1704.

Any suggestions or do I just have a bad system that should have been fixed three years ago?

EDIT:  Was doing a 4 GB  file transfer and half way through the speed dropped from 52 to 5 Mbps, and the router is only 18 feet away.  I guess the Inspiron 5748 series has a poor wifi?   The Vostro  is about 25 feet away and has a floor and two walls and has had no issues (other than being outdated).

Ray