Prusa i3 with Bowden extruder: failure to bridge infill/top surfaces

I recently finished a large Prusa i3 (build surface 300x200x300 mm) and have been struggling to get it to print correctly ever since. Originally, I had a wade geared extruder (standard one packaged with the Prusa i3 on GitHub) and was able to print pretty successful prints. The problem was that the x-carriage was carrying enough mass that there was a 2 mm difference in z-position between the max/min x-location and the center of the build plate. I then converted to a Bowden (using the same extruder/hotend with adaptor parts and some push fit connectors) and was able to print a few things well (spiral vases, thin wall calibration item, 100% infill objects) but whenever I have any infill less than 100%, my printer is incapable of building a top surface. I attached two examples of this. The ooze bane calibration piece shows two different infill percentages: 30% on the left, and 15% on the right. Both situations, the printer fails to produce continuous threads of plastic. I attempted increasing and decreasing the filament diameter (from 1.60-1.80 and everywhere in between) in Cura, but still it made these crappy bridged gaps. I tried increasing and decreasing the temp (from 190-230), lowering the print speed, increasing layer height...all resulted in the same garbage. If it weren't for the top surfaces, the prints would look pretty nice, but the printer cannot bridge any gap whatsoever. Any ideas on things I could tweak to get it to succeed? Thanks!

You didn't say how many bottom and top layers you have your slicer setup for.
I use 70 to 80 percent infill and 3 bottom and 4 to 6 top layers for an object like that

An object like what? The ooze calibration object? For that I've tried printing with as little as 2 bottom/top layers, and as many as 8. The only difference between the two resultant prints were the number of infill layers the machine printed. It still entirely failed to bridge the top layer.

Try raising the flow rate, maybe. Adding more top solid infill layers wouldn't hurt, either.

My current thought is it is a cooling issue. I had my hotend fan in a duct, but I couldn't feel it blowing hardly at all. I removed the duct and hung the fan with a temporary zip tie rig, and I'm getting the best prints I've seen since switching to bowden.

I ordered a different hot end barrel (with a thicker PTFE liner) and a blower fan to increase cooling even more. I'll update after I receive/install these new components.