Clearly, there is no upward slope - at least not any simple or easily discernible way. To try to make some sense of this, I color coded the points for different time periods. That is shown in Graph 2.
Once the light blue points are segregated, it's pretty easy to see that the remaining points reside mostly in a horizontal band.
Here is the arrangement.
1952 -60 Yellow - Eisenhower
1961 -68 Dark Purple - Kennedy-Johnson
1969 -71 Green - Preamble to the Great Inflation
1972 - 82 Light Blue - The Great Inflation
1983- 92 Dark Blue - Beginning of the Great Stagnation
1993 - 00 Red - The Clinton Stability
2001-08 Dark Blue - Culmination of the Great Stagnation
2009 on Pink - The Great Recession to now
As it turns out, the Red and Dark Purple points are hard to differentiate. [if you right click on the graph and select "Open link in new window," you can blow up the graph by clicking "Control" and the "+" sign several times.] The red points are more closely clustered and surrounded by the purple. There are the hearts of your two little moderations.
Originally I had the entire 1983 - 08 period in dark blue, then decided to highlight the Clinton years in red to see if anything stood out. What we find is a short period of the greatest stability in the record, regarding both of these two variables.
So, the data tells that for the post 1952 period, there is no robust relationship between debt growth and inflation. In fact, except for the Great Inflation period, the relationship might even be slightly negative. The 1969-71 period, just prior to the Great Inflation, has the unique combination of lower debt growth and higher inflation than any other time in the data set.
Also, the Great Recession and it's aftermath are unlike anything else we've seen in recent decades.
Bottom line, though, is that a rate of CPI inflation of 3 +/- 1% is associated with the entire range of debt growth in the modern era. And, if debt growth is a serious factor in health of the economy, inflation targeting is close to meaningless as a policy tool.