Last September I rode south from White Haven, and have ridden the Lehigh Gorge Trail more times than I can count. It's an o.k. section, but it can get stinky in the gorge on a warm, humid day. Trail conditions are fine. South from JT there is a gap. Here is how I got around it:
https://ridewithgps.com/routes/23517634
Picked up the trail again in Bowmanstown. From there to N. Catasaqua is not really scenic, but trail conditions are decent. There is another big gap in N. Catasaqua. Also, at 62.7 on the above map, that road is one way in the wrong direction, and it's narrow. I did not take and instead plotted a course around it to pick up the trail where shown on the map. Lot's of traffic along this trail gap. From there to Easton the trail is poorly marked in places and can be a bit confusing. It's shaded, but some sections were like riding flat single track.
The map isn't complete, but I went all the way to Easton, where I got a motel. The next morning I took the trail on the PA side of the river to Riegelville then crossed into NJ. There is a Roebling designed and built bridge there. That section of the trail can be a bit gravelly in places, but there are some decent views of the river. Followed quiet roads on the NJ side that I am well familiar with to Milford the crossed back into PA and took the trail about 1.5 miles south to reach a campground near Upper Black Eddy.
The next morning I went back to Milford, NJ and took a road toward Frenchtown to pick up the D&R feeder trail to Lambertville. It's my understanding that the D&L trail on the PA might still be damaged/rough in places from past floods. If it is, you don't want to have to ride PA 32. I hate that road and will only ride it in an emergency. Minimal to no shoulder and too many impatient drivers. A cyclist was killed on that road several years back. The D&R trail has a good surface of crushed limestone and is well shaded, but not that interesting. In the summer vegetation blocks most of the river views. Bull's Island recreation area along the way is the most interesting spot. There is a pedestrian bridge across the river which has a nice view.
Can't help you beyond that as I have never ridden either the D&R or the D&L south of Lambertville or New Hope. I have seen most of the D&R between Lambertville and I-95 while driving on NJ 29. It looks perfectly benign.
Can you now take your bike on the Pennsylvanian?
This was taken between Bethlehem and Easton:
https://www.flickr.com/photos/105349...7685810338542/
There were some portions along this stretch that were narrower.
Cannot remember if this was north or south of Easton:
https://www.flickr.com/photos/105349...7685810338542/