Hi there: For a few years I've been dealing with the frustration of an inaccurate gas gauge on my '68 Valiant after I replaced the tank and sending unit with moderately-priced aftermarket items. I've had the same issue of "drops from Full like a rock within 30 miles" that several other people have dealt with. That wasn't all of it, though: Issue #2: leaked past the sending unit seal even though everything was new. Tipped off that the replacement lock rings are too thin. Replaced with original, leak stopped. Issue #3 leaked past the filler tube seal even though it was replaced when the tank was(2 years prior). Pulled the tank again today to inspect and found the seal was beginning to shrink and split even though it had the part # and DPCD symbol made into it JUST LIKE THE ORIGINALS. Issue #4 observed today that the dust seal(the one around the filler tube at the trunk floor) that I replaced almost exactly one year ago with one from DMT, is beginning to dry and crack. He claims they are EPDM just like the originals...but the factory didn't use THIS version of EPDM because theirs lasted 40+ years. I may request a refund or replacement. So, I've had too many issues. Last week I ordered another sending unit and DMT's supposedly better filler tube seal. Pulled the tank today after pumping out 12 gallons of gas...the gauge indicated 1/4 tank btw. I decided to test the new sending unit on the car before installing it. Guess what....it's readings matched the one I took out. Both were WAY off. Tonight, I realized I had everything needed to make some scientific tests to determine of the sending units are all defective the way people claim they are. I was already convinced they were. I have the dash out of my 68,000 mile Dart sitting waiting to go back in, so I used it and a jumper pack to power things. I powered the gauge regulator with the jump pack and then created a ground loop through the sending unit and gauge back to the jump pack. The test results were informative. I marked each sending unit body at the point where the gauge read Full, 3/4, 1/2, and Empty. The first surprise that neither sender displayed the sudden "drop" from Full. While the points that each indicated the chosen level on the gauge were slightly different between the two, again, neither displayed erratic readings. Based on the tight grouping of F, 3/4, 1/2 and 1/4...then the spread of space down to E, I would say that the sending units are designed closely enough to original that they would work correctly. Both sending units took a relatively significant amount of travel to reach and cross through the E mark and both did somewhat before the float arm reached the bottom stop. I also discovered that the replacement Spectre tank I bought back then has a reinforcing rib made into it that the original doesn't have in that location and as a consequence the float arm hits it before reaching the bottom stop. So, this has helped convince me that the issue is elsewhere. Mopar only gives specs on the resistance at Full and Empty and the spec at empty is plus or minus 12 ohms, so it's pretty 'loose". I checked the ground path through the metal fuel line on my car at it passed with flying colors. Here's my opinion: I think the problem is in the fuel gauges. That Dart and my '66 Chrysler both spent their lives garaged out of the sun and heat and both gauges read accurately..for the '60's. On the other hand, the Plymouth baked outside it's entire life and I've had other problems with the cluster being warped and dried out. Someone on a board also claimed that the gauges could be damaged over time and they were pretty quickly ignored. Anyway, I'll post some pictures in the next post. Thanks for reading.