Hello monstertrucker and welcome to TRCF.
From what I can gather, the Spectrum SR300 receiver is your problem.
Found some SR3100's on ebay for ya.Spektrum customer service; Turns out the SR300 ($50) is a sport receiver (ie. a "park flyer" for RC cars/trucks) not a "full range" receiver (especially when using it in a gasoline powered vehicle. Swapping out the SR300 with a SR3100 solved my problem.
At Tamiya USA they recommend you...
https://www.tamiyausa.com/product/it...oduct-id=45037*Always use a receiver with BEC when operating TEU-103BK. Using Non-BEC receivers may result in malfunction of receiver.
This is the receiver that I use with all the TLU- ESC's...
Futaba BEC Receiver - R162JE
Hope this post has been of some help.